IC-NRLF 


SB    2b 


William  Street,  New  York  City,  while  the  Underpinning  Operations  Were  at 
Their  Height  in  1915 


WILEY  ENGINEERING   SERIES— No.  2 

MODERN 
UNDERPINNING 

DEVELOPMENT,    METHODS 
AND   TYPICAL   EXAMPLES 

BY 

LAZARUS  WHITE,  C.E. 
EDMUND  ASTLEY  PRENTIS,  JR.,  E.M. 


FIRST  EDITION 
FIRST  THOUSAND 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:    CHAPMAN   &   HALL,    LIMITED 

1917 


Copyright,  1916,  by 
LAZARUS  WHITE  and  EDMUND  A.  PRENTIS,  JR. 


PUBLISHERS  PRINTING  COMPANY 
207-217  West  Twenty-fifth  Street,  New  York 


PREFACE 

THE  authors  of  this  volume,  being  familiar  with  the 
development  of  the  art  of  underpinning  from  its  rather 
crude  methods  in  1900  to  its  present  highly  developed 
state,  and  having  unusual  opportunities  to  gather 
valuable  first-hand  material  through  the  generosity  of 
Smith,  Hauser  &  Maclsaac,  Inc.,  whose  contract 
involved  the  greatest  amount  of  underpinning  inci- 
dental to  any  one  contract  on  subway  work,  have  been 
impelled  to  make  this  fund  of  information  available 
to  engineers  and  contractors. 

During  the  progress  of  construction  on  William 
Street  throughout  two  years,  great  pains  were  taken  to 
photograph  the  essential  steps  in  underpinning,  sup- 
plementing these  with  drawings  and  scientifically 
altered  photographs.  It  was  felt  that  one  good  illus- 
tration was  worth  many  pages  of  description,  and 
every  effort  was  made  to  gather  a  complete  set.  Just 
enough  text  was  added,  it  is  hoped,  to  sufficiently 
supplement  the  illustrations. 

As  the  engineer  has  usually  only  a  very  limited 
time  at  his  disposal,  the  book  is  so  arranged  that  almost 
without  the  text  he  may  quickly  get  correct  and  ac- 
curate ideas  as  to  the  proper  methods  of  underpinning. 

As  the  present  work  of  construction  on  the  New  York 


364740 


VI  PREFACE 

subways  is  drawing  to  a  close,  it  is  to  be  feared  that 
the  really  wonderful  progress  made  in  construction 
during  this  period  of  about  sixteen  years  will  be  im- 
perfectly recorded  and,  perhaps,  in  a  large  measure 
lost.  This  progress  was  due  to  the  combined  efforts 
of  the  best  contracting  and  engineering  talent  to  be 
found  in  any  community.  The  authors  will  be  suffi- 
ciently rewarded  if  they  are  the  means  of  preserving 
the  acquired  knowledge  of  only  one  phase  of  this 
gigantic  work. 

LAZARUS  WHITE. 

EDMUND  ASTLEY  PRENTIS,  JR. 

DECEMBER,  1916. 


WILEY   ENGINEERING   SERIES 


THE  Wiley  Engineering  Series  will  embrace  books  devoted 
to  single  subjects.  The  object  of  the  series  is  to  place  in  the 
hands  of  the  practising  engineer  all  the  essential  information 
regarding  the  particular  subject  in  which  he  may  be  inter- 
ested. Extraneous  topics  are  excluded,  and  the  contents  of 
each  book  are  confined  to  the  field  indicated  by  its  title. 

It  has  been  considered  advisable  to  make  these  books  man- 
uals of  practice,  rather  than  theoretical  discussions  of  the  sub- 
jects treated.  The  theory  is  fully  discussed  in  text-books,  hence 
the  engineer  who  has  previously  mastered  it  there  is,  as  a  rule, 
more  interested  in  the  practice.  The  Wiley  Engineering  Series 
therefore  will  present  the  most  approved  practice,  with  only 
such  theoretical  discussion  as  may  be  necessary  to  elucidate 
such  practice. 


TABLE   OF   CONTENTS 

CHAPTER   I 

PAGE 

GENERAL  ASPECTS — UNDERPINNING  DEFINED — PAYMENT  FOR  UNDER- 
PINNING   i 

CHAPTER   II 
DEVELOPMENT  OF  UNDERPINNING  AND  METHODS 7 

CHAPTER   III 
SHORES,  NEEDLES,  AND  FOUNDATION  REENFORCEMENT 19 

CHAPTER   IV 
UNDERPINNING  PIERS,  PILES,  AND  WEDGING 43 

CHAPTER  V 

SPECIFIC  EXAMPLES  OF  UNDERPINNING 58 

146,  148,  and  150  William  Street 58 

I45"1 55  William  Street 60 

Bank  of  America 63 

National  City  Bank 69 

Lord's  Court  Building 72 

135  William  Street .  76 

Kuhn-Loeb  Building 78 

Underpinning  Elevated-Railroad  Columns          85 

APPENDIX 

UNDERPINNING  IN  ROCK 89 

SPECIAL  ARRANGEMENT  OF  PIT  BOARDS 91 

ix 


LIST  OF  ILLUSTRATIONS 

William  Street  looking  south  from  Maiden  Lane,  New  York  City  Frontispiece 

PAGE 
PLATE  I — Method  of  shoring  used  in  1902  during  subway  construction 

in  New  York  City 8 

PLATE  2 — Method  known  as  "protection"  used  above  water-level  .  .  n 
PLATE  3 — Combination  of  underpinning  and  protection  methods  used 

above  water-level 12 

PLATE  4 — Method  of  underpinning  below  water-level  for  deep  excavation  14 
PLATE  5 — Building  supported  on  a  continuous  concrete  wall  built  in  four- 
foot  sections  beneath  a  new  grillage 15 

PLATE  6 — Shores  used  in  1902  during  subway  construction  in  New 

York  City 20 

PLATE  7 — Composite  steel  and  timber  shore 22 

PLATE  8 — Clamp  on  square  cast-iron  column  of  250  tons  before  being 

concreted 24 

PLATE  9 — Typical  needling  method  showing  underpinning  pier  and 

wedging 25 

PLATE  10 — Method  of  needling  25o-ton  cast-iron  column  .  .  .  .27 
PLATE  n — Showing  cross-section  of  needle-beams  composed  of  15" 

H-beams  and  12"  I-beams 28 

PLATE  12 — Reenforcing  rods  placed  for  grillage  in  Woodbridge  Building  .  32 
PLATE  13 — Original  footing  of  one  of  the  columns  of  the  Kuhn-Loeb 

Building,  52-54  William  Street,  New  York 33 

PLATE  14 — Reenforcing  steel  and  I-beams  in  grillage  for  Kuhn-Loeb 

Building  before  concreting 35 

PLATE  15 — The  grillage  of  the  Kuhn-Loeb  Building  after  being  concreted  36 

PLATE  16 — Crossed  I-beams  between  brick  piers 38 

PLATE  17 — Reenforcement  with  dowels  and  rods 38 

PLATE  18 — Grillage  detail  of  brick  pier  of  typical  small  building  showing 

beams  and  dowels 39 

PLATE  19 — Grillage  for  typical  small  building  showing  beams,  cross-ties, 

dowels,  etc.,  before  concreting 40 

PLATE  20 — Grillage  for  typical  small  building  after  concreting  ...  41 
PLATE  21 — Showing  use  of  lattice  girders  for  grillage  purposes  before 

being  concreted 41 

xi 


xu  LIST   OF    ILLUSTRATIONS 

PAGE 

PLATE  22 — Method  of  placing  foot  block  and  wedges  to  hold  bottom 

boards  in  underpinning  pit  until  set  is  complete 44 

PLATE  23 — Showing  start  of  underpinning  pit  under  spread  footing  .      .  45 

PLATE  24 — Showing  underpinning  pit  under  spread  footing      ....  46 
PLATE  25 — Method  of  transferring  column  load  from  old  foundation  or 

new  grillage  to  new  underpinning  concrete  pier 47 

PLATE  26 — Sleeve  for  connecting  sections  of  steel  pipe  used  as  piles    .      .  48 

PLATE  27 — A  good  type  of  riveted  steel  pipe  for  underpinning  purposes  .  49 

PLATE  28 — Pile-hammering  rig 50 

PLATE  29 — Jacking  rig,  consisting  of  hydraulic  pump,  flexible  copper  pipe, 

and  rams 52 

PLATE  30 — Pile-mucking  implements         53 

PLATE  31 — Pile-settlement  curve 55 

PLATE  32 — Improved  method  of  loading  piles  beneath  building  foundations  56 

PLATE  33 — Burning  apparatus  in  operation 57 

PLATE  34 — Showing  exterior  longitudinal  18"  I-beams   and  15"  I-beam 

needles  with  lashings  to  prevent  spreading 59 

PLATE  35 — 145-155  William  Street,  showing  columns,  grillage,  under- 
pinning piers,  etc 61 

PLATE    36 — Showing   concrete    steel   grillage,    underpinning   piers,    etc. 

Typical  for  moderate-sized  buildings 62 

PLATE  37 — Grillage  and  underpinning  piers  for  145-155  William  Street  .  64 

PLATE  38 — Bank  of  America,  showing  underpinning 65 

PLATE  39 — Plan  of  underpinning  of  the  Bank  of  America 67 

PLATE  40 — Showing  brick  columns,  continuous  concrete  base,  V-shaped 
concrete  enclosing    crossed   15"  I-beams  and  the  practically  com- 
pleted underpinning,  excavation  for  subway  cut  started     ....  68 
PLATE  41 — Photograph  of  Bank  of  America,  showing  overhang  of  the 

old  original  spread  foundations,  etc 70 

PLATE  42 — National  City  Bank  Building,  showing  its  underpinning  and 

the  subway  cut         73 

PLATE   43 — Showing   substitution   of    14"   steel   concrete   piles   for   old 

wooden  ones  which  had  to  be  removed  in  the  Lord's  Court  Building.  75 

PLATE  44 — Underpinning  of  135  William  Street 77 

PLATE  45 — Kuhn-Loeb  Building,  showing  its  underpinning      ....  79 

PLATE  46 — Plan  of  the  underpinning  of  the  Kuhn-Loeb  Building        .      .  83 
PLATE  47 — Showing  method  of  temporarily  carrying  elevated  railroad 

columns 86 

PLATE  48 — Plan  of  underpinning  of  elevated  railroad  columns       ...  87 


MODERN    UNDERPINNING 


CHAPTER  I 

GENERAL    ASPECTS— UNDERPINNING    DEFINED— PAYMENT 
FOR    UNDERPINNING 

WHEREVER  the  foundation  of  a  building  or  struc- 
ture is  endangered  by  a  neighboring  excavation,  the 
need  for  underpinning  arises.  Most  frequently,  the 
excavation  endangering  the  neighboring  structure  is 
that  for  a  new  building  planned  to  go  deeper  than  its 
old  neighbor.  But  the  excavation  which  endangers  the 
largest  number  of  buildings  along  a  street  is  that  for 
subways  or  tunnels.  Indeed,  were  it  not  for  the  recent 
developments  in  underpinning  methods,  many  such 
subways  would  not  be  possible,  except,  perhaps,  at 
almost  prohibitive  cost  and  inconvenience  to  property- 
owners. 

Methods  and  costs  of  underpinning  have  a  vital 
bearing  on  many  engineering  problems,  as  railroads 
and  tunnels  can  now  be  placed  close  to  very  costly 
buildings  resting  on  any  kind  of  foundation,  and  on 
almost  any  material,  without  seriously  endangering 
them  or  adding  a  prohibitive  amount  to  the  cost  of 
construction. 

1 


2  MODERN    UNDERPINNING 

In  the  past  many  improvements  had  to  be  aban- 
doned because  of  opposition  from  building  owners  who 
feared  serious  damage  to  property  and  business  if  the 
excavation  incident  to  such  improvements  were  made. 
Also  many  costly  locations  were  substituted  for  more 
convenient  ones  so  as  to  shun  the  neighborhood  of 
expensive  structures. 

In  many  instances  in  the  past  buildings  have  been 
seriously  damaged  and  the  business  carried  on  in  them 
much  inconvenienced  because  of  the  insufficiency  or 
lack  of  underpinning  or  the  crude  and  expensive 
methods  in  vogue  up  to  a  few  years  ago.  Often 
large  chances  had  to  be  taken  because  no  reasonable 
method  of  underpinning  was  known  for  the  difficult 
cases.  The  sad  experience  gained  in  these  instances 
has  caused  much  opposition,  delay,  and  even  defeat  of 
needed  improvements  which  we  now  know  could  be 
safely  carried  through. 

The  building  of  the  subways  of  New  York  un- 
doubtedly contributed  more  to  the  advancement  of 
the  art  of  underpinning  than  all  other  causes  com- 
bined. Almost  every  conceivable  case  is  here  met  and 
solved.  Miles  of  excavations  were  made  close  to  and 
much  deeper  than  the  adjacent  buildings  on  all  kinds  of 
foundations,  solid  and  shelving  rocks,  earth  and  quick- 
sand. Some  of  the  buildings  had  to  be  carried  bodily 
and  set  upon  the  subway  roof.  The  structures  varied 
from  unimportant  little  buildings  up  to  one  of  twenty- 
one  stories,  and  included  miles  of  elevated  railroads. 


UNDERPINNING  3 

The  contracts  for  the  construction  of  the  subways 
up  until  1911  did  not  specifically  provide  for  the  un- 
derpinning of  adjacent  buildings,  but  obligated  the  con- 
tractors to  safeguard  the  buildings,  incidentally  with 
the  excavation.  This  worked  fairly  well,  but  in  many 
cases  led  to  the  assumption  of  too  great  risks  on  the 
part  of  the  contractors,  which  was  difficult  to  remedy, 
as  the  city  did  not  have  authority  to  order  underpin- 
ning since  there  was  no  item  for  this  in  the  contract. 

In  1911  the  form  of  subway  contracts  was  radically 
changed  from  lump  sum  to  unit  prices,  and  under- 
pinning items  were  introduced  into  the  Lexington 
Avenue  contracts.  This  gave  the  engineer  the  req- 
uisite authority  to  safeguard  the  buildings  by  providing 
specific  payment  for  the  same. 

The  underpinning  items  for  nearly  all  the  contracts 
are  on  the  front-foot  basis,  with  different  items  for 
buildings  above  a  certain  number  of  stories,  usually  six. 
It  was  also  attempted  to  differentiate  between  under- 
pinning and  maintenance,  maintenance  being  an  in- 
complete underpinning  or  protection  of  the  fronts  of 
buildings  by  cut-off  walls  constructed  with  or  in  ad- 
vance of  the  excavation.  This  differentiation  is  a 
difficult  one,  and  some  of  the  later  contracts  contain  an 
item  for  each  building  or  group  of  buildings  likely  to 
be  affected  by  the  excavation,  the  contractor  bidding  a 
price  including  all  the  necessary  work  of  safeguarding 
the  buildings.  This  was  found  to  work  much  better. 

On  the  new  subway  system  the  number  of  linear 


4  MODERN   UNDERPINNING 

feet  underpinned  was  about  75,000  feet.  The  cost  was 
about  $6,350,000.  On  the  William  Street  subway  alone 
the  cost  for  3,970  feet  of  underpinning  was  about 
$612,000  Some  of  the  individual  buildings  are  about 
as  follows: 

The  Woodbridge  Building,  100  William  Street, 
fourteen  stories,  126  feet  front,  on  fine  sand  and 
clay,  $25,000. 

The  Kuhn-Loeb  Building,  52  and  54  William  Street, 
twenty-one  stories,  69  feet  front,  on  fine  clay  and  sand, 
$32,000. 

The  National  City  Bank,  55  Wall  Street,  eight 
stories,  172  feet  front,  on  fine  sand  and  clay,  $30,000. 

The  New  York  Cotton  Exchange,  60  Beaver  Street, 
ten  stories,  1 18  feet  front,  on  fine  sand  and  clay,  $24,000. 

The  usual  specifications  for  underpinning  as  given 
in  the  subway  contracts  are  here  abstracted,  as  they 
are  the  only  ones  of  the  kind  to  be  found. 

11  SUBDIVISION  5,  SECTION  69.  The  contractor  at 
the  beginning  of  construction  will  be  required  to  safely 
and  permanently  underpin,  and  during  construction 
will  be  required  to  maintain,  protect,  and  secure  such 
buildings  along  the  line  of  the  railroad  as  are  enumer- 
ated in  Schedule  Item  4-Q. 

Underpinning  Defined 

"  By  underpinning  is  meant  such  method  of  con- 
struction as  will  transmit  the  foundation  loads  directly 
through  the  underpinning  structure  to  such  lower  level 


UNDERPINNING  5 

as  is  necessary  to  secure  the  buildings  and  which  will 
relieve  the  adjacent  ground  from  improper  lateral 
pressures.  The  underpinning  shall  be  designed  to 
furnish  a  safe  and  permanent  support  for  each  inde- 
pendent building.  To  accomplish  this  result,  the 
contractor  shall  use  such  methods  of  underpinning, 
pneumatic  or  otherwise,  as  special  conditions  may 
require  and  the  engineer  shall  approve." 

11  Before  the  work  is  proceeded  with,  the  contractor 
shall  submit  to  the  engineer  drawings  in  duplicate 
indicating  the  proposed  typical  and  special  methods 
of  underpinning." 

Payment  for   Underpinning 

"  SECTION  No.  70.  Payment  for  safely  and  perma- 
nently underpinning  at  the  beginning  of  construction 
and  for  maintaining,  protecting,  and  securing  during 
construction  the  buildings  enumerated  in  Schedule 
Item  4-Q  will  be  made  at  the  prices  stipulated  in  such 
Schedule  Item,  which  prices  shall  be  deemed  to  include 
payment  for  all  work,  labor,  and  material  of  whatever 
nature  required  in  connection  with  safely  and  perma- 
nently underpinning  at  the  beginning  of  construction 
and  for  maintaining,  protecting,  and  securing  the  entire 
building  or  groups  of  buildings,  such  as  side  walls, 
both  interior  and  along  transverse  streets;  partition 
walls,  both  parallel  and  perpendicular  to  the  building 
front;  interior  columns  and  any  other  work  which 
may  be  required,  and  no  allowance  will  be  made  therefor 


6  MODERN    UNDERPINNING 

under  any  other  Schedule  Item  or  otherwise.  The 
prices  are  not  to  include  the  payment  for  underpinning 
or  for  maintaining,  protecting,  and  securing  vaults, 
areaways,  retaining  walls,  stoops,  or  porches,  but  the 
payment  for  such  work,  when  required,  shall  be  deemed 
to  .be  included  in  the  prices  stipulated  for  excavation 
in  Schedule  Items  I  and  2.  If  ordered  by  the  enginner, 
the  contractor  shall  dig  test  pits  alongside  the  building 
foundations.  Payment  for  such  test  pits  will  be 
made  to  the  contractor  as  and  at  the  price  stipulated 
in  Schedule  Item  2-A.  (See  Section  No.  427.)" 


CHAPTER   II 

DEVELOPMENT   OF   UNDERPINNING   AND   METHODS 

ABOUT  ten  years  ago  the  common  method  of 
supporting  buildings  while  neighboring  excavations 
were  under  way  was  to  employ  "  shores,"  which  were 
set  up  in  long,  inclined  lines  against  the  wall  endan- 
gered, as  shown  on  Plate  No.  i. 

This  crude  method,  although  usually  preventing 
collapse,  often  seriously  cracked  the  structure,  and  large 
settlements  occurred  despite  the  liberal  use  of  screw- 
jacks  at  the  base  of  the  shores. 

Another  method  much  more  effective  was  to  use 
needles,  which  were  horizontal  beams  carrying  the 
structure,  while  the  neighboring  excavation  was  being 
made.  The  needles  were  inserted  in  holes  or  niches 
cut  for  them,  and  were  supported  on  blocking,  the 
load  being  obtained  by  the  use  of  wedges  or  screw- 
jacks.  Later  the  wall  was  usually  carried  on  new 
brick  piers  containing  two  wedging  stones,  which  were 
separated  by  steel  wedges  driven  home  until  the  piers 
relieved  the  needles  of  their  load.  This  method  of 
needling  is  much  more  effective  than  shoring,  but 
has  many  drawbacks,  as  will  be  shown  in  another 
chapter. 

When  compressed-air  caissons  were  introduced  for 


PLATE  No.  I.     Method  of  Shoring  Used  in  1902  during  Construction  of  the 

Subway  in  New  York  City 

Note  cracks  in  the  brickwork.      Compare  this  with  the  frontispiece  as  to 
street  obstruction,  etc. 


DEVELOPMENT    OF    UNDERPINNING   AND    METHODS      9 

foundations  of  buildings,  a  great  advance  was  made. 
Small,  compressed-air  cylinders,  about  three  feet  in 
diameter,  were  introduced  for  supporting  the  walls  of 
the  neighboring  building  while  the  caissons  for  the 
new  one  were  being  sunk.  These  small  caissons  were 
usually  sunk  directly  underneath  the  walls  to  rock 
or  hard-pan,  were  wedged  up  and  constituted  real 
underpinning.  But  this  method  is  expensive,  requir- 
ing the  use  of  compressor  plant,  air  locks,  etc.,  and 
is  not  flexible. 

The  next  step  was  the  use  of  pipes,  steel  or  wrought 
iron,  and  filled  with  concrete,  instead  of  caissons. 
These  were  driven  or  jacked  down  a  suitable  depth 
directly  below  the  wall  to  be  underpinned  and  con- 
stituted a  great  advance.  This  improvement  was 
introduced  by  Jules  Breuchaud  and  J.  B.  Goldsborough. 

In  underpinning  a  building  it  is  often  necessary  to 
continue  the  foundation  to  a  lower  level  with  a  new 
masonry  pier,  usually  of  concrete.  To  excavate  for 
these  piers  immediately  below  the  foundation  was 
very  difficult  with  ordinary  vertical-driven  sheeting, 
owing  to  the  lack  of  head  room.  A  great  forward  step 
was  made  when  horizontal  sheeting  or  well-curbing  was 
introduced  by  J.  C.  Meem,  for  excavation  below 
foundations.  Here  the  boards  are  placed  plank  by 
plank  horizontally  in  pits  4  to  5  feet  square.  Very 
little  ground  is  lost  and  the  pits  can  be  sunk  almost 
anywhere,  and  to  any  depth,  above  ground-water  level. 
When  the  desired  depth  or  ground  water  is  reached, 


10  MODERN    UNDERPINNING 

from  within  them  sectional  pipe  piles  can  be  con- 
veniently driven  to  almost  any  depth  if  necessary. 

Great  security  and  flexibility  were  obtained  when 
the  method  of  reenforcing  and  tying  together  individual 
foundations  by  means  of  steel  grillages  fastened  to  their 
footings  and  concreted  in  with  them  was  intro- 
duced. This  in  effect  places  a  new  and  better  founda- 
tion for  the  building  to  be  underpinned  and  allows 
almost  any  desired  combination  of  piers  and  piles  to 
be  used.  It  often  allows  the  building  to  be  under- 
pinned entirely  from  the  outside,  thus  saving  many 
costly  removals  of  machinery  and  much  loss  of 
valuable  space  which  previously  was  thought  to  be 
unavoidable. 

The  use  of  piles  for  underpinning  has  been  much 
facilitated  by  the  introduction  of  sectional  riveted 
steel  and  wrought-iron  pipe  piles,  improvements  in 
hydraulic  jacks,  electric  winches  for  hammer  driving, 
earth  augers  and  miniature  orange-peel  buckets,  etc., 
described  in  detail  elsewhere. 

With  the  careful  methods  of  sheeting  the  sides  of 
excavations  that  are  now  in  use,  it  is  necessary  to 
underpin  only  those  portions  of  the  building  that  are 
immediately  adjacent  to  the  excavation.  In  many 
cases,  if  the  structure  is  some  distance  away  from  the 
excavation  and  grade  is  above  water-level,  it  is  not 
necessary  to  underpin  at  all,  the  method  known  as 
protection  being  used. 

This  consists  of  a  continuous  or  semi-continuous 


DEVELOPMENT   OF    UNDERPINNING   AND    METHODS     11 

masonry  cut-off  wall  between  the  excavation  and  the 
building  footings,  as  shown  in  Plate  No.  2. 


PLATE  No.  2.     Method  Known  as  "Protection"  Used  above  Water-level 
The  building  is  supported  on  the  original  soil,  because  no  ground  is  lost.     The 
wall  is  so  constructed  that  when  braced  it  serves  as  sheeting  and  cut-off 
for  the  trench  or  excavation 

Sometimes  a  combination  of  underpinning  and 
protection  is  used,  the  underpinning  being  carried  to  a 
one-to-one  slope  from  the  bottom  of  the  excavation 
and  a  cut-off  wall  built,  as  shown  on  Plate  No.  3. 


DEVELOPMENT   OF   UNDERPINNING   AND   METHODS     13 

It  is  very  important  to  provide  a  tight  cut-off  between 
the  building  and  the  excavation,  no  matter  what 
methods  of  underpinning  are  used,  in  order  to  protect 
the  interior  columns  and  basements.  This  becomes 
of  vital  importance  when  the  excavation  is  carried 
below  ground- water  level,  as  then  the  cut-off  walls 
become  impracticable.  Tongue  and  grooved  wooden 
sheeting  and  various  types  of  interlocking  steel  sheeting 
are  then  employed,  depending  on  the  local  conditions, 
and  should  be  driven  down  sufficiently  deep  to 
prevent  the  soil  from  boiling  up,  as  is  shown  in 
Plate  No.  4. 

An  excellent  example  of  a  building  completely 
underpinned  by  piers  placed  by  means  of  4^4'  hori- 
zontally sheeted  pits  is  shown  on  Plate  No.  5. 

Before  underpinning  is  started  a  careful  examina- 
tion of  the  building  should  be  made,  particularly  in 
regard  to  its  defects.  This  is  in  order  to  know  as 
closely  as  may  be  the  condition  of  the  building  in  case 
a  controversy  should  arise.  The  examination  should 
consist  of  an  exact  written  description  and  should  not 
consist  of  photographs  only,  which  would  not  be  con- 
clusive legal  evidence. 

A  good  example  of  the  form  for  such  an  examination 
is  that  employed  by  the  Public  Service  Commission  in 
New  York  City  in  connection  with  subway  construction. 
The  following  is  an  excerpt  from  one  of  their  exami- 
nations : 


PLATE  No.  4.     Method  of  Underpinning  below  Water-level  for  a  Deep 

Excavation 

Sectional  steel  concrete  piles  when  wedged  to  new  grillage  carry  the  column 
loads,  the  sheeting  in  front  prevents  the  loss  of  soil  during  the  excavation, 
and  thus  protects  the  interior  walls  and  columns  of  the  building 


PLATE  No.  5.     Building  Supported  on  a  Continuous  Concrete  Wall  Built  in 

Four-foot  Sections  beneath  a  New  Grillage 

The  wall  also  acts  as  sheeting  for  the  excavation,  and  is  twenty-five  feet  in 

height 


16  MODERN    UNDERPINNING 

EXAMINATION  OF  BUILDING 

" Building:  135  William  Street,  Borough  of  Man- 
hattan, New  York  City. 

"Description:  Sixteen-story  granite,  brick,  and 
terra-cotta. 

11  Occupied  as:  Offices. 

" Owner:  Royal  Baking  Powder  Co.,  135  William 
Street,  New  York  City. 

" Present  (representing  owners):  Mr.  M.  Feiner, 
present  during  examination. 

"Present  (representing  contractors):  J.  Edward 
Kloberg. 

"Examined  by:  Harry  M.  Leon,  Jr.,  Assistant  Engi- 
neer, per  Leo  B.  Meister,  stenographer  for  Public 
Service  Commission. 

"Date:  May  17-18,  1915." 

EXTERIOR 

"  Front  Wall  on  William  Street:  First,  second,  and 
third  stories,  granite;  fourth  to  twelfth  stories,  inclusive, 
brick ;  upper  stories,  terra-cotta. 

''First  Story:  Horizontal  mortar  joints  along  top  and 
bottom  of  granite  stone  along  south  end  of  north 
cellar  window  need  repointing. 

"  Second  to  Fourth  Story:  O.  K. 

" Fifth  Story:  Third  window  south:  lower  pane 
cracked. 

"Sixth  to  Twelfth  Story:  O.  K. 


DEVELOPMENT   OF    UNDERPINNING   AND    METHODS     17 

"Thirteenth  Story:  A  few  interior  terra-cotta  blocks 
cracked  into  two  pieces. 

"Fourteenth  Story:  Fourth  window  north :  fine  crack, 
top  of  brick  panel  below  sill,  two  feet  from  north  end, 
extends  vertically  downward  through  middle  of  one 
brick,  then  north  along  mortar  joint  one  inch,  then 
extends  vertically  downward  along  mortar  joint  on 
one  course  of  brick,  then  extends  vertically  downward 
through  middle  of  one  brick.  A  few  terra-cotta  blocks 
cracked  into  two  pieces. 

"Fifteenth  Story:  A  few  individual  terra-cotta  blocks 
cracked  into  two  pieces. 

"Sixteenth  Story:  O.  K. 

"South  building  line  from  sidewalk  to  top  of  third 
story  shows  a  maximum  i-inch  vertical  filled  joint. 
From,  this  point  to  roof  shows  /^-inch  open  vertical 
joint." 

The  next  step  is  the  determination  of  the  loadings 
of  the  various  columns  or  walls.  These  can  very 
often  be  obtained  from  the  architect's  plans,  or  can  be 
calculated  in  the  usual  way.  In  this  connection  it 
might  be  noted  that  the  allowable  floor  loadings  from 
the  building  code  of  New  York  City  give  loads  to  be 
provided  for,  but  are  more,  possibly  by  10  or  20  per 
cent,  than  the  actual  loads.  In  order  to  give  a  rough 
idea  of  the  various  column  and  wall  loads  that  are  en- 
countered, it  might  be  said  that  ordinary  25-foot  wide 
five-story  brick  and  stone  buildings  have  column 


18  MODERN    UNDERPINNING 

loads  of  30  to  40  tons  at  the  front  wall,  and  the 
side  walls  carrying  the  floors  run  about  12  tons  to 
the  linear  foot  at  the  base.  A  rough  method  of  cal- 
culating the  loads  on  the  front  wall  is  to  allow  i  to 
\y%  tons  per  story  per  front  foot,  which  may  be  distrib- 
uted to  the  columns  according  to  their  distance  apart. 
The  solid  masonry  office  buildings  that  were  built 
thirty  years  ago  have  tremendous  column  loads,  some 
eight-story  buildings  having  all  columns  as  heavy  as 
500  tons,  of  which  90  per  cent  is  actual  dead  weight, 
while  the  modern  twenty-story  steel  skeleton  building 
has  also  about  500  tons  on  each  column,  though  it 
should  be  borne  in  mind  that  each  building  is  a  separate 
problem. 

The  design  of  the  underpinning  is  rather  simple, 
but  particular  care  and  experience  are  needed  for 
the  actual  construction.  Generally  speaking,  under- 
pinning piers  are  designed  so  as  to  give  a  pressure 
on  the  soil  of  four  tons  per  square  foot,  while  14- 
inch  steel  concrete  piles  can  safely  be  assigned  a  load 
of  30  to  40  tons,  testing  the  piles  to  50  per  cent  more 
than  the  assigned  load. 


CHAPTER   III 

PRELIMINARY   WORK 

Shores,  Needles,  and  Foundation  Reenforcement 

IN  most  cases,  before  the  new  foundation  or  the 
underpinning  proper  can  be  placed  beneath  the  walls 
or  piers  endangered  by  neighboring  excavations,  it  is 
necessary  to  place  some  form  of  preliminary  support. 
This  preliminary  support  can  be  divided  into  three 
general  types — shores,  needles,  and  grillages. 

Shores  are  inclined  braces  placed  against  the  walls 
or  piers  of  buildings,  and  a  few  years  ago  were  very 
frequently  used,  and  are  effective  when  applied  to 
light  buildings.  They  can  be  readily  placed  in  niches 
cut  in  the  brickwork,  the  lower  ends  resting  on  screw- 
jacks,  used  to  tighten  up  the  shores  and  to  take  up 
settlement.  They  usually  consist  of  long  12  x  12 
timbers,  which  can  be  readily  shown  to  be  very  weak 
as  columns  and  as  placed  are  decidedly  lacking  in 
lateral  stiffness.  They  have  to  be  very  numerous  to 
support  any  considerable  load  and  are  usually  very 
much  in  the  way.  Formerly,  when  no  better  method 
was  known,  they  frequently  blocked  streets  and  side- 
walks. When  compared  with  other  devices  they  are  an 
expensive  and  cumbersome  way  of  supporting  build- 
ings. An  example  of  shoring  is  shown  on  Plate  No.  6. 

19 


20 


MODERN    UNDERPINNING 


In  the  case  of  a  building  burned  out  by  a  fire, 
shores  may  be  useful  to  prevent  the  collapse  of  danger- 
ous walls  while  they  are  being  torn  down,  and  they 
may  also  be  useful  to  support  light  walls  in  the  altera- 


PLATE  No.  6.     Shores  Used  in  1902  during  the  Construction  of  Subway, 

New  York  City 
Note  total  removal  of  sidewalk.     Compare  with  modern  methods 

tion  of  building  fronts,  although  in  this  case  vertical 
posts  supporting  short  horizontal  beams  previously  set 
in  holes  in  the  walls  or  columns  are  more  usual.  In  a 
few  instances  shores  may  be  used  to  advantage  in 
connection  with  other  means  to  counteract  the  tendency 
of  the  building  to  move  horizontally  or  to  give  a  remote 
support  at  the  beginning  of  the  regular  underpinning 


PRELIMINARY   WORK  21 

operations.  For  heavy  buildings,  composite  timber 
and  steel  shores  have  been  used  to  good  advantage, 
the  foot  of  the  shore  resting  on  a  concrete  block  and 
the  top  in  a  niche  in  the  masonry;  steel  wedges  driven 
home  will  transfer  as  much  of  the  load  as  is  desirable 
to  the  shores,  or  screw-jacks  may  be  used.  In  general, 
steel  wedges  in  underpinning  operations  are  much  to  be 
preferred  to  screw-jacks.  They  give  greater  stability 
and  can  hardly  overload  the  member  or  unduly  strain 
or  rack  the  building  as  jacks  have  repeatedly  done.  In 
the  effort  to  take  up  settlement  jacks  have  often 
taken  up  too  much  and  cracked  the  building. 

A  good  example  of  a  shore  is  shown  on  Plate  No.  7, 
though  this  took  a  very  minor  part  in  the  operations. 

The  second  method  of  preliminary  support  is  that 
where  needles  are  used  in  the  place  of  shores.  Needles 
are  vastly  more  effective  and  adaptable  than  shores, 
and  very  many  ingenious  systems  of  needling  have  been 
employed  in  underpinning  operations. 

In  general,  they  are  horizontal  beams,  usually  steel 
I-beams,  so  placed  as  to  relieve  the  foundations  of  a 
wall  or  pier  of  its  load  and  to  transmit  the  loads  to 
temporary  blocking  or  piling  on  either  side  of  the  wall 
or  pier,  allowing  space  for  removing  the  old  foundation 
and  substituting  a  new  one.  Knowing  the  load  and 
span,  the  size  of  the  beams  is  readily  computed. 
Where  the  walls  are  to  be  supported  by  needles,  holes 
are  cut  at  intervals  through  the  wall  and  the  needles 
inserted  at  convenient  intervals  after  the  walls  are  re- 


22  MODERN   UNDERPINNING 

enforced  by  small  I-beams  or  stones  bricked  in  to  take 
and  distribute  the  bearing  from  the  beam  and  to  prevent 
rupture  of  the  wall. 

Where  isolated  columns  or  piers  are  to  be  supported 
the  common  practice  is  to  cut  niches  into  the  columns 


PLATE  No.  7.     Composite  Steel  and  Timber  Shore 

Steel  channels  are  rigidly  bolted  to  timber  separator  and  wedged  to  foundation 
and  concrete  abutment 

fitting  the  I-beams.  This  sometimes  weakens  the 
masonry  pier,  so  that  it  is  advisable  rather  to  fasten  a 
clamp  or  bracket  to  the  column.  This  can  readily  be 
done  by  timber  or  steel  clamps  bolted  fast  or  a  concrete 
collar  can  readily  be  cast  to  the  column  after  a  few 
dowels  and  a  little  reenforcement  have  been  placed. 


PRELIMINARY   WORK  23 

Clamps  for  supporting  cast-iron  and  steel  columns 
have  to  be  very  carefully  made,  particularly  where 
heavy  concentrations  have  to  be  carried.  Steel  columns 
are  more  readily  fastened  to  as  rivets  may  be  removed 
and  the  holes  used  for  bolting  clamps  or  brackets  to 
them.  Usually  these  brackets  are  heavy  channels 
fastened  with  a  sufficient  number  of  bolts  to  provide 
the  necessary  shearing  strength. 

Cast-iron  columns  are  the  most  difficult  to  fasten 
to.  A  good  method  is  to  drill  clear  through  them  and 
insert  long  steel  pins  to  prevent  the  clamps  from 
slipping  on  the  column.  Several  clamps  may  be  used, 
each  bearing  on  one  or  more  pins.  Great  rigidity  can 
be  secured  by  concreting  in  the  clamps;  this  is  well 
illustrated  by  Plate  No.  8. 

The  greatest  difficulty  with  needles  is  to  provide  a 
sufficient  bearing  area,  for  their  abutments  or  supports. 
It  is  usually  necessary  to  occupy  considerable  space  in 
the  interior  of  the  building  for  the  inner  supports, 
which  is  often  difficult  to  obtain,  and  may  necessitate 
the  moving  of  much  machinery,  etc.  Again,  the 
exterior  ends  of  the  needles  may  project  over  an 
excavation,  necessitating  the  building  up  of  a  great 
height  of  cribbing  or  the  driving  of  groups  of  piles  with 
platforms  to  provide  exterior  abutments  for  the  needles. 
To  overcome  this  difficulty,  in  one  instance,  the  needles 
were  used  as  true  levers,  the  fulcrum  being  near  the  build- 
ing and  the  projecting  ends  counterweigh  ted  to  balance 
the  wall  loads,  but  this  does  not  appear  to  be  good  practice. 


PLATE  No.  9.     Typical  Needling  Method  Showing  Underpinning  Pier  and 

Wedging 

Needles  are  designed  to  support  the  column  while  new  foundation  is  placed 

below 


26  MODERN    UNDERPINNING 

An  effective  and  safe  method  of  needling  a  building 
front  is  to  place  long  beams  parallel  to  the  front,  both 
inside  and  outside,  with  pairs  of  transverse  needle 
beams  resting  on  them,  each  pair  carrying  a  column. 
The  longitudinal  beams  are  carried  on  blocking  and 
the  needles  wedged  from  them  to  take  the  load.  This 
method  is  well  shown  on  Plate  No.  9. 

A  very  heavy  system  of  needling  is  shown  on  Plate 
No.  10.  Here  the  subway  passes  directly  under  a  heavy 
ten-story  building  whose  cast-iron  columns  carried 
loads  up  to  250  tons,  sub-grade  being  20  feet  below 
the  column  footings.  As  previously  explained,  heavy 
brackets  were  fastened  to  the  columns,  the  brackets 
bearing  against  transverse  2O-inch  I-beams  carried 
by  heavy  pairs  of  1 5-inch  H-beams.  These  H-beams 
were  reenforced  by  1 2-inch  I-beams  grouted  in  be- 
tween them,  making  a  very  stiff  unit,  as  shown  in 
Plate  No.  II,  being  broad  and  low  with  no  tendency 
to  overturn.  It  is  of  course  not  economically  designed 
as  regards  the  steel  used,  but  it  is  nevertheless  very 
cheap  because  the  members  are  not  drilled  or  cut  and 
can  easily  be  placed  in  position,  easily  dismantled, 
and  the  steel  recovered  in  perfect  condition.  The 
needles  were  carried  oh  heavy  timber  towers,  from  which 
they  were  wedged.  No  jacks  were  used  in  the  trans- 
ferring of  the  load  to  the  needles,  the  wrought-iron 
wedges  proving  very  efficient. 

Although  needles  give  an  effective  preliminary 
support,  enabling  new  foundations  to  be  placed,  they 


28 


MODERN    UNDERPINNING 


have  many  disadvantages,  and  their  disadvantages 
multiply  rapidly  and  become  very  serious  when  heavy 
loads  have  to  be  carried.  Where  the  loads  are  over 
200  tons,  the  needles  become  very  heavy  and  it  is 


PLATE  No.  n.     Showing  Cross-Section  of  Needle-Beams  Composed  of  15" 

H-Beams  and  12"  I-Beams 
This  construction  saved  much  steel  detailing  and  proved  very  rigid  and  stable 

difficult  to  secure  sufficient  area  for  the  necessary 
cribbing  and  blocking  which  serve  as  abutments  for 
the  needles,  the  bearing  being  usually  figured  at  about 
2  tons  per  square  foot.  These  abutments  and  the 
needles  themselves  will  often  be  seriously  in  the  way 
of  the  occupants  of  the  building  and  those  engaged 
on  the  construction  alongside  the  building.  When  the 
column  loads  run  as  high  as  500  tons  the  size  of  the 
needles  may  become  enormous  and  a  sufficient  bearing 


PRELIMINARY   WORK  29 

area  for  the  blocking  practically  impossible.  The 
disadvantages  of  needling  buildings  have  been  apparent 
for  a  long  time,  but  it  has  only  been  within  the  last 
few  years  that  better  methods  of  preliminary  support 
have  come  into  use,  and  with  them  the  danger  of  a 
serious  collapse  has  with  careful  work  almost  dis- 
appeared. 

In  brief,  these  new  methods  take  the  foundation  and 
support  of  the  buildings  as  they  are  and,  instead  of 
removing  them  before  placing  new  foundations  or 
underpinning,  add  to  them  and  strengthen  them  so  as 
to  allow  the  new  supports  to  be  more  freely  placed 
below  them.  The  foundation  so  reenforced  is  brought 
up  to  the  standard  of  a  scientific  and  properly  designed 
footing  of  the  continuous  grillage  type — for  instance, 
that  of  a  building  on  a  continuous  mat  of  concrete  reen- 
forced by  steel  I-beams  or  rods.  Often,  buildings  are  on 
isolated  footings  of  I-beam  grillages  which  can  readily 
be  made  continuous  by  filling  the  gap  between  them 
with  similar  construction. 

Exposure  of  a  great  many  foundations  of  all  types 
along  the  New  York  subways  clearly  shows  that  the 
best  type  of  footings  for  buildings,  with  the  exception 
of  caissons  or  steel  concrete  piles,  is  that  of  the  grillage, 
composed  of  two  layers  of  I-beams  thoroughly  embedded 
in  concrete,  provided  a  sufficient  bearing  area  on  the 
soil  was  originally  allowed.  These  grillages  or  footings 
may  be  isolated  for  individual  columns  or  connected 
along  the  exterior  walls.  There  seems  to  be  an  im- 


30  MODERN   UNDERPINNING 

pression,  and  it  is  given  considerable  emphasis  in  some 
text-books,  that  isolated  footings  proportioned  to  the 
load  are  much  safer  than  continuous  footings,  which 
of  necessity  cannot  be  uniformly  loaded  per  square 
foot  of  bearing  area.  There  may  have  been  some  justifi- 
cation for  this  when  masonry  without  steel  reenforce- 
ments  was  used,  as  then  cracking  of  the  foundations 
was  feared  and  could  be  mathematically  demonstrated. 
But,  with  a  foundation  properly  reenforced,  there  is 
practically  no  danger  of  cracking,  the  continuous 
foundation  being  vastly  superior  to  the  isolated  one. 
Even  in  the  case  of  old  masonry  foundation  laid  up 
in  lime  mortar,  very  little  cracking  of  foundations  was 
observed  when  on  a  yielding  sand. 

A  good  type  of  foundation  on  earth  is  one  whose 
footings  underneath  the  exterior  walls  consist  of  a  con- 
tinuous mat  of  I-beams  and  concrete  with  a  generous 
bearing  area,  say  4  tons  per  square  foot,  so  constructed 
as  not  to  encroach  on  the  street  or  neighboring  prop- 
erty. The  interior  foundations  may  be  isolated  mats 
of  I-beams  and  concrete,  or,  better,  a  continuous  mat 
between  columns. 

Such  a  building  is  easily  underpinned  and  will  not 
suffer  much  from  neighboring  excavations;  it  may  be 
underpinned  with  concrete  piers  or  piles  placed  directly 
beneath  the  footings,  and  little  disturbance  or  incon- 
venience to  the  occupants  of  the  building  will  be  felt 
if  the  underpinning  operations  are  in  competent  hands. 

Where  a  building  has  not  the  ideal  type  of  founda- 


PRELIMINARY   WORK  31 

tion  for  underpinning  purposes,  the  aim  should  be  to 
add  to  it  sufficiently  to  approach  the  ideal.  This  can 
be  well  illustrated  by  the  Woodbridge  Building. 

This  building,  a  thirteen-story  structure,  approached 
very  closely  to  the  subway  structure,  necessitating  the 
underpinning  of  its  front  wall,  carried  by  eight  columns, 
each  loaded  with  about  435  tons.  Each  column  was 
founded  upon  a  grillage  consisting  of  two  layers  of 
I-beams,  the  lower  one  paralleling  the  building  front. 
These  grillages  approached  within  three  or  four  feet 
of  each  other.  To  diminish  the  risks  of  underpinning 
an  additional  grillage  was  decided  upon,  although  it 
was  considered  quite  feasible  to  underpin  each  grillage 
individually,  as  they  were  of  generous  proportions. 

First  the  I-beams  were  well  stripped  of  their 
enveloping  concrete,  exposing  the  sides  of  the  outside 
I-beams  of  the  upper  row  and  the  ends  of  the  lower  row 
as  shown  on  Plate  12.  Next  holes  were  drilled  in 
the  concrete  between  the  beams  for  a  great  number 
of  hooked  dowels  which  were  grouted  in.  Then  i^4- 
inch  rods  were  cut  to  fit  the  spaces  of  the  upper 
row  of  I-beams.  Rods  were  also  placed  in  the 
gaps  of  the  lower  row,  their  ends  being  supported 
by  short  rods  wedged  between  the  I-beams,  and 
inclined  rods  were  butted  against  the  upper  flanges  of 
the  upper  I-beams.  The  cutting  of  the  rods  was 
easily  accomplished  with  the  acetylene  torch.  A  form 
was  set  up  and  all  the  steel  thoroughly  embedded  in  a 
generous  block  of  rich  concrete.  This  grillage  took 


PRELIMINARY   WORK  33 

about  ^/2  tons  of  steel  rods  and  70  cubic  yards  of  con- 
crete and,  although  generous  in  size  and  strength,  was 
economical  as  to  cost.  It  is  believed  to  be  the  first 


PLATE  No.  13.     Original  Footing  of  One  of  the  Columns  of  the  Kuhn-Loeb 

Building,  52-54  William  Street 

Below  upper  beams  is  another  layer  of  I-beams,  then  30"  of  foundation 
concrete  resting  on  fine  sand 

heavy    underpinning    grillage    built    entirely    of    steel 
rods  and  concrete. 

The  heaviest  grillage  built  for  underpinning  pur- 
poses is  probably  that  of  the  Kuhn-Loeb  Building, 
a  modern  twenty-one-story  steel  structure  with  column 
loads  of  over  500  tons  each.  The  front  wall  of  this 
building  is  carried  by  five  columns  supported  by  I-beam 


34  MODERN    UNDERPINNING 

grillages  about  17  feet  below  curb  level,  and  founded 
on  a  very  fine-grained  sand  three  feet  above  water 
level.  The  grillages  encroached  about  six  feet  upon 
the  street  and  the  future  subway  structure,  and  the 
building  was  so  underpinned  as  to  allow  the  cutting 
off  of  these  encroachments. 

The  two  columns  at  the  south  end  rested  upon  a 
huge  "cantilever"  girder,  in  turn  resting  upon  a  trans- 
verse layer  of  1 8-inch  I-beams.  The  other  columns 
of  the  front  row  were  founded  upon  a  layer  of  2O-inch 
I-beams  resting  upon  a  transverse  layer  of  1 5-inch 
I-beams,  which  in  turn  were  founded  upon  a  3O-inch  layer 
of  concrete.  This  structure  is  clearly  shown  on  Plate  13. 

The  grillage  beams  were  carefully  stripped  of  con- 
crete. Some  of  them  were  found  to  be  badly  rusted 
where  hot  water  from  a  boiler  had  penetrated  the 
somewhat  porous  enveloping  concrete.  This  carries  the 
lesson  that  grillage  beams  should  be  thoroughly 
enveloped  in  concrete  (a  dense  mortar  is  best). 

To  make  the  layers  of  I-beams  continuous,  beams 
were  cut  with  an  acetylene  torch  to  closely  fit  between 
the  outside  of  the  webs  of  the  lower  layer  and  others 
to  overlap  the  ends  of  the  upper  layer.  In  addition 
hooked  dowels  and  reenforcing  rods  were  used  to 
strengthen  the  outward  projection  of  the  grillage.  To 
spread  the  column  loads  directly  over  the  reenforced 
grillage,  buttresses  were  built  outward  from  the  steel 
columns,  which  were  stripped  for  the  purpose.  The 
resulting  grillage,  shown  on  Plate  No.  14,  was  strong 


in 

i 

•8 


Og 

<u  U 

•5  o> 

dl 


CQ 


c/) 
bo 


36  MODERN    UNDERPINNING 

enough  to  fully  take  the  upward  thrust  from  the  new 
steel  underpinning  piles  which  were  subsequently 
placed.  These  reactions  are  very  considerable,  as  a 
group  of  five  in  a  4  x  4  foot  area  may  be  much  above 


PLATE  No.  15.     The  Grillage  of  the  Kuhn-Loeb  Building  after  Concreting 
with  Underpinning  Piers  Marked  Out  and  Numbered 
View  is  from  same  position  as  Plate  No.  14 

200  tons.  The  entire  structure  was  concreted  in  with 
a  mixture  rich  in  mortar,  as  shown  on  Plate  15.  The 
additional  steel  used  was  8^  tons;  additional  concrete 
55  cubic  yards* 

There  is  always  some  uncertainty  as  to  just  where 
to  place  the  reenforcing  steel  of  an  underpinning  grillage. 
Some  contend  for  the  lower  portion,  others  the  upper, 


PRELIMINARY   WORK  37 

and  each  or  both  are  logical,  depending  upon  what 
theory  of  the  shifting  of  the  column  loads  during  under- 
pinning operations  is  adopted.  If  the  underpinning  is 
first  placed  between  the  columns  and  securely  wedged 
and  the  columns  settle  slightly,  the  grillage  will  be  in 
tension  -on  the  upper  side,  which  is  probably  the  normal 
case.  Because  of  unequal  settlements  and  continuity, 
the  stresses  may  be  reversed,  and  thus  it  was  thought 
best  to  reenforce  top  and  bottom  to  take  care  of  all 
contingencies.  The  safest  guide  appears  to  be  a  good 
sense  of  proportion  and  the  placing  of  the  additional 
steel  so  as  to  make  up  for  defects  in  the  original  footing 
and  to  thoroughly  piece  them  out. 

Just  previous  to  the  introduction  of  steel  frames 
to  buildings,  columns  were  commonly  carried  on  heavy 
piers  or  pyramids  of  brickwork.  By  cutting  niches  into 
those  to  be  underpinned,  inserting  heavy  crossed  I- 
beams  and  concreting  them  in,  the  piers  may  be  con- 
nected rigidly,  as  shown  on  Plate  No.  16,  and  then 
are  readily  underpinned.  An  older  type  of  foundation, 
and  one  which  gives  excellent  results,  is  the  continuous 
masonry  wall  laid  up  in  a  trench.  Often  these  walls, 
though  adequate  for  their  purpose,  are  not  sufficiently 
strong  to  stand  the  stresses  of  underpinning  operations. 
By  scraping  out  their  joints,  inserting  dowels  and 
longitudinal  reenforcing  rods  or  beams,  and  con- 
creting them  in  with  a  rich  mixture,  the  walls  are  readily 
reenforced,  as  in  the  case  of  the  Bank  of  New  York, 
shown  on  Plate  No.  17. 


PLATE  No.  16.     Crossed  I-Beams  between  Brick  Piers 

The  beams  were  placed  in  niches  carefully  cut  for  them  and  then  securely 

concreted  in 


PLATE  No.  17.     Reenforcement  of  Dowels  and  Rods 

Used  for  reenforcing  wall  laid  up  in  lime-mortar  and  subsequently 

concreted  in.      Bank  of  New  York 


PRELIMINARY   WORK 


39 


The  commonest  buildings  underpinned  are  those 
of  five  or  six  stories  with  isolated  piers  and  carrying 
comparatively  small  loads,  20  to  40  tons.  As  they  are 
often  poorly  built,  they  are  the  more  easily  injured 


PLATE  No.  18.     Grillage  Detail  for  Brick  Pier  of  Typical  Small  Building 

Showing  Beams  and  Dowels 
When  surrounded  by  concrete  this  is  a  very  effective  and  rigid  construction 

and  often  give  more  concern  than  heavy  structures. 
The  piers  or  footings  for  these  buildings  are  readily 
connected  by  employing  small  I-beams  and  dowels, 
fastened  front  and  back  as  shown  on  Plates  No.  18, 
19  and  20.  After  being  concreted  they  spread  the  load 
over  a  much  larger  area  and  tie  the  footings  together 
securely,  and  are  then  readily  underpinned. 


40 


MODERN    UNDERPINNING 


Lattice  girders  have  been  extensively  used  for 
grillages.  They  have  the  advantages  of  being  continu- 
ous and  readily  connected  together  in  tight  places. 
Such  a  use  of  a  lattice  girder  at  123  William  Street 


PLATE  No.  19.     Typical  Steel  Grillage  for  Small  Building,  Showing  Beams, 

Cross-Ties,  Dowels,  etc.,  before  Concreting 
Appearance  after  concreting  shown  in  Plate  No.  20 

is  shown  on  Plate  No.  21.  Here  the  interior  girder 
was  placed  under  a  barber-shop  floor  which  was 
tunneled  under  and  supported  by  I-beam  props. 
The  advantages  of  the  lattice  girder  have  been  largely 
lost  since  the  acetylene  torch  for  cutting  steel  has 
come  into  extensive  use.  With  an  assortment  of 


PLATE  No.  20.     Typical  Grillage  for  Small  Building  after  Concreting,  Showing 

Small  Pipes  Left  for  Grouting  the  Underpinning  Piers 

View  from  same  position  as  Plate  No.  19 


PLATE  No.  21.     Showing  the  Use  of  Lattice  Girders  for  Grillage  Purposes 

before  Concreting 
Lattice  girders  are  useful  when  space  is  too  small  to  place  long  beams 


42  MODERN    UNDERPINNING 

I-beams  and  rods  a  grillage  can  readily  be  made  to  suit 
almost  any  condition,  the  beams,  rods,  dowels,  etc., 
being  cut  to  length  as  actually  found  to  be  needed  when 
the  foundation  is  stripped.  When  the  Kuhn-Loeb 
grillage  was  being  made  up,  a  torch,  set  up  adjacent 
to  the  work,  was  kept  continuously  in  use  for  days 
cutting  up  the  steel  to  the  desired  length. 

The  function  of  dowels  in  steel  concrete  grillages 
for  underpinning  is  very  important.  They  develop 
great  strength,  not  through  their  actual  shearing 
strength,  which  may  not  figure  very  high,  but  by 
keeping  the  concrete  gripped  to  the  old  masonry  and 
thereby  developing  a  tremendous  friction  grip. 


CHAPTER   IV 

UNDERPINNING    PIERS,    PILES,    AND   WEDGING 

PITS  for  the  new  underpinning  piers  can  sometimes 
be  sunk  by  the  old-fashioned  vertical-driven  sheeting 
with  which  we  are  all  familiar,  but  cannot  be  used 
where  there  is  scant  head  room.  This  method  has  now 
been  almost  entirely  supplanted  by  the  horizontal 
well-curbing  method,  which  was  referred  to  in  a  pre- 
vious chapter. 

By  this  method  pits  can  be  made  almost  any  size 
up  to  12  feet  square,  but  are  usually  4  or  5  feet,  and 
have  been  sunk  60  feet  through  sand  and  clay,  using 
only  2-inch  sheeting.  The  most  conveniently  sized  plank 
to  use  is  2  x  8  inches,  and  as  the  work  must  be  done 
with  considerable  nicety  in  order  not  to  lose  ground, 
it  is  advisable  to  use  plank  finished  on  all  four  sides. 
A  skilled  gang  of  workmen  will  sink  about  6  feet  per 
shift  of  eight  hours  in  sandy  ground  clear  of  boulders, 
though  sometimes  as  much  as  15  feet  have  been  sunk, 
sinking  always  stopping  at  water-level,  when  other 
methods  must  be  resorted  to. 

Unless  the  pit  is  under  a  needled  column,  when 
pit  sinking  can  be  started  directly,  it  is  necessary  to 
dig  carefully  in  underneath  the  foundation  the  neces- 
sary distance,  putting  in  temporary  piles  or  posts 

43 


44 


MODERN    UNDERPINNING 


where  needed  to  make  up  for  the  lost  bearing  area, 
and  to  carefully  sheet  the  sides  of  the  excavation, 
packing  behind  the  boards  with  soil  where  necessary. 


PLATE  No.  22.     Shows  Method  of  Placing  Foot  Block  and  Wedges  to  Hold 
Bottom  Boards  in  Underpinning  Pit  Until  Set  Is  Complete 

Enough  ground  is  then  dug  out  to  place  a  set  of  hori- 
zontal planks,  which  are  each  in  turn  carefully  packed 
and  hammered  into  place,  being  temporarily  held  until 
the  set  is  complete,  by  a  foot  block  and  wedge,  as 
shown  on  Plates  Nos.  22,  23,  and  24. 


PIERS,    PILES,    AND    WEDGING 


45 


When  the  pit  has  been  sunk  the  required  depth, 
it  is  concreted  to  within  two  feet,  or  other  convenient 


PLATE  No.  23.     Showing  Start  of  Underpinning  Pit  under  a  Spread  Footing. 

Only  small  fraction  of  original  bearing  area  is  lost  during  this  operation.    New 

foundation  to  be  placed  in  pit  is  wedged  up  before  another  pit  is  started. 

working  distance,  from  the  bottom  of  the  foundation, 
and    allowed    to    set.     Then   it   is   wedged    up.     This 


46 


MODERN    UNDERPINNING 


important  operation,  which  conveys  the  load  of  the 
column  to  the  pier,  is  sometimes  done  by  means  of  a 
small  masonry  pier  and  wedging  stones,  or,  better,  by 
the  use  of  steel  I-beams  and  wrought-iron  wedges, 


PLATE  No.  24.     Showing  Start  of  Underpinning  Pit  under  Spread  Footing. 

Crossed  15"  I-beams  are  embedded  in  concrete  between  brick  piers 
Pit  is  for  the  purpose  of  providing  space  and  head  room  to  drive  and  wedge 

piles  to  foundation 

the  whole  concreted  and  carefully  grouted  up,  as  shown 
on  Plate  No.  25. 

In  case  the  bearing  area  of  the  pit  is  insufficient, 
or  in  case  it  is  necessary  to  go  below  ground-water 
level,  the  pier  is  supplemented  with  sectional  steel-pipe 
piles.  These  are  driven  by  a  dropping  weight  or  a 


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48 


MODERN    UNDERPINNING 


hammer   if  sufficient   head    room  is  available,  or  by 

hydraulic  rams. 

The  pipes  while  being  driven  are  mucked  out  every 

foot  or  two  to  make  the  driving  easier  and  to  prevent  the 
pipe  from  buckling,  and  when  driven 
are  concreted,  tested,  wedged  up  directly 
to  the  foundation  or  grillage,  if  possible, 
and  the  pit  concreted  and  carefully  grouted. 
The  sectional  pile  pipe  used,  generally 
12-inch  or  1  4-inch  in  diameter,  is  of  va- 
rious kinds.  Ordinary  wrought-iron  pipe 
with  cast-iron  or  steel  couplings  is  very 
satisfactory,  but  perhaps  expensive  unless 
the  pipe  is  obtained  second-hand.  This 
is  shown  on  Plate  No.  26. 

An  equally  satisfactory  pipe,  and  one 
which  is  more  easily  handled,  is  the  sheet- 
steel,  lap-riveted  pipe.  This  comes  in  any 
desired  length,  usually  2  feet.  With  a 
thickness  of  only  %4  inch,  surprising 

PLATE  No.  26.    strength   is  obtained,  an  empty  pipe  hav- 
withstood   a  load  of  90  tons  without 


c  onecting 

Sections    of    rupture,  though   50  tons  is  a  more  usual 

Used  as  Piles    load.     The  starter  or   first   length   of  the 
pile  is   usually   reenforced   with   an  extra 
thickness  of  metal  to  prevent  the  buckling  of  the  cut- 
ting edge,  as  shown  on  Plate  No.  27. 

A  gang  can  drive  and  muck  about  twenty  feet  of 
pile  in  ground  without   boulders  in   eight  hours  with 


50  MODERN    UNDERPINNING 

a  drop-hammer  rig.  This  consists  of  a  " nigger-head" 
winch,  a  few  snatch  blocks,  a  graphite  lubricated 
hemp  rope  and  a  hammer  about  9  inches  diameter 
and  400  or  500  pounds  weight  dropping  2  or  3 


PLATE  No.  28.     Pile-Hammering  Rig 
Piles  were  driven  a  few  feet  at  a  time  and  then  mucked  out 

feet    on    to   a  steel   pile  cap  and  guided  by  hand,  as 
shown  on  Plate  No.  28. 

When  the  necessary  head  room  for  hammering  is 
not  available,  a  hydraulic  ram  is  used.  The  best  rig 
for  this  purpose  is  an  independent  pump  good  for  about 
13,000  pounds  per  square  inch  with  a  ^-inch  plunger, 
so  that  two  men  can  easily  pump,  and  a  4X-inch  diam- 


PIERS,    PILES,    AND   WEDGING  51 

eter  ram  about  20  inches  high,  the  available  extension 
being  about  1 1  inches  and  the  weight  about  175  pounds. 
The  ram  is  connected  to  the  pump  by  ^-inch  flexible 
copper  tubing  with  steel  fittings.  This  copper  pipe 
should  be  annealed  from  time  to  time  to  destroy  the 
crystallization  which  comes  from  constant  bending  and 
which  would  result  in  a  break.  This  whole  rig  is  very 
light,  and  is  easily  portable  by  a  gang  which  can 
drive  and  muck  from  4  to  25  feet  per  eight 
hours  with  a  general  average  of  8  feet  for  ground 
without  boulders.  This  apparatus  is  shown  on  Plate 
No.  29. 

The  mucking  is  accomplished  by  means  of  earth 
augers  and  miniature  orange-peel  buckets.  The  augers 
are  attached  to  a  muck  stick  of  j^-inch  pipe  cut  into 
lengths  of  about  4  feet,  with  a  universal  joint  for  each 
section  so  that  it  can  be  conveniently  handled  in  a 
restricted  space.  The  orange-peel  bucket  is  attached 
to  the  same  muck-stick  so  that  it  can  be  pressed  against 
the  soil  while  the  closing  rope  is  pulled,  or  a  new  type 
of  bucket  can  be  used,  which  is  operated  very  con- 
veniently by  means  of  two  ropes,  the  lowering  one 
being  attached  to  a  1 2-pound  ball  which  acts  as  a 
hammer  to  drive  the  open  prongs  of  the  bucket  into 
the  soil  before  the  closing  rope  is  pulled.  The  mucking 
implements  are  shown  on  Plate  No.  30.  When  the 
soil  is  fine-grained  a  piece  of  leather  riveted  to  the 
upper  blades  of  the  earth  auger  is  a  big  help  to  prevent 
the  muck  from  slipping  between  the  space  between  the 


PIERS,    PILES,    AND    WEDGING 


53 


upper  and  lower  blades,  by  acting  as  a  clap  valve. 
Water- jetting  or  blowing  out  the  muck  from  piles  is  a 
quick  and  efficient  method  if  piles  are  being  driven 
in  the  open,  but  in  the  vicinity  of  buildings  is  likely 


PLATE  No.  30.     Pile-Mucking  Implements 

Augers  with  jointed  rods  commonly  used.     Small  orange-peel  buckets  useful 
for  heavy  sand  and  gravel,  especially  when  operated  by  winch 

to  cause  trouble  by  removing  too  much  material  from 
the  pile  and  causing  a  flow  of  the  soil,  and  conse- 
quently a  settlement  of  the  structure.  Care  must 
always  be  taken  not  to  muck  below  the  bottom  of  the 
pile,  for,  although  the  pile  may  drive  easier,  lost  ground 
may  result. 

Piles    up    to    30    feet    in    length    are    conveniently 


54  MODERN    UNDERPINNING 

driven,  and  when  they  are  driven  as  deep  as  it  is  neces- 
sary to  go,  they  are  concreted.  This  has  to  be  done 
with  a  great  deal  of  care  because  the  water  in  the  pile 
will  wash  out  the  cement,  leaving  merely  sand  and 
gravel  in  the  pile.  The  best  way  is  to  bail  or  pump 
the  water  out  of  the  pile  and  then  concrete.  If  this 
is  impossible  or  unsafe,  for  sometimes  the  removal  of 
the  water  causes  the  soil  to  rise  in  the  pile,  a  bottom- 
dumping  bucket  is  used.  When  the  pile  is  concreted 
it  is  next  tested. 

This  means  that  the  concreted  piles  are  jacked  down 
until  they  give  a  predetermined  resistance  of  40,  60, 
or  80  tons,  or  more,  measured  by  means  of  a  pressure 
gauge  on  the  pump.  They  are  then  wedged  up,  pro- 
viding the  pit  is  not  too  deep,  in  which  case  the  pit  is 
concreted  and  the  concrete  wedged  as  before  described. 

When  the  pile  is  wedged  directly,  a  cap,  generally 
a  short  length  of  steel  channel,  is  placed  on  top  of  the 
pile  and  from  it  an  I-beam  is  wedged  with  wrought- 
iron  wedges  (usually  ^.  x  2^  x  16  inches)  against  the 
bottom  of  the  foundation  by  driving  in  the  wedges  hard 
with  an  eight-pound  hammer. 

In  this  way  a  load  of  about  8  tons  can  be  immedi- 
ately transmitted  to  the  pile.  If  the  pile  is  to  carry  from 
30  to  40  tons,  the  usual  load  of  12-  or  1 4-inch  piles,  it 
is  now  known  that  there  must  be  a  further  settlement 
of  the  foundation  before  this  load  can  be  sustained. 
Furthermore,  we  have  found  by  a  series  of  careful 
experiments,  one  of  the  results  of  which  is  given  in  the 


PIERS,    PILES,    AND    WEDGING 


55 


I, 


o  5 


accompanying  curves  shown  on  Plate  No.  31 ,  that  a  pile, 
not  on  rock,  will  repeatedly  settle  with  repeated  ap- 
plications of  the  load.      This  is  due  not  only  to  the 
elasticity  of  the  pile  itself,  but  mainly 
to  the  fact  that  the  bulb  of  pressure 
which  forms  at  the  base  of  the  pile 
(and  the  shape  of    which  has   been 
developed  by  J.  F.   Greathead)   has 
to  be  reformed  by  further  penetra- 
tion after  it  is  destroyed  by  the  re- 
lease of  the  load. 

To  overcome  this  difficulty,  piles 
are  now  wedged  up  without  releas- 
ing the  load,  by  a  new  method  for 
which  a  patent  has  been  applied  for 
by  one  of  the  authors.  When  the 
pile  has  been  tested  to  refusal  at  the 
predetermined  test  load  without  re- 
leasing the  load,  two  pieces  of  I-beams 
are  cut  to  fit  and  are  wedged  up 
one  on  each  side  of  the  jack  which 
rests  on  a  special  pile  cap.  When 
the  wedging  is  completed  the  jack 

t  .  PLATE  No.  31.      Pile 

is  released.     By  this  means,  40  tons        Settlement  Curve 

can  be  immediately  transmitted    to 

the  pile,  as  has  often  been   proven 

with  a  strain  gauge.     This  method 

will   reduce    the  settlement   of   a  structure  materially 

and  is  shown  on  Plate  No.  32. 


20        40         60 

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Note  rebound  and  set- 
tlement after  each 
loading  of  pile 


PIERS,    PILES,    AND    WEDGING 


57 


An  indispensable  adjunct  in  underpinning  opera- 
tions is  an  apparatus  for  cutting  iron  and  steel  by 
means  of  a  flame.  This  consists  of  a  torch  connected 
by  means  of  two  flexible  armored  hoses  to  tanks  of 


PLATE  No.  33.     Burning  Apparatus  in  Operation 
Portable  rig  found  to  be  very  useful 

compressed  oxygen  and  a  rich  hydrocarbon  gas,  a 
picture  of  which  is  here  shown.  The  two-wheel  go- 
cart  for  hauling  the  apparatus  around  is  very  con- 
venient, especially  if  a  central  spindle  with  a  ring  at 
the  top  is  added  so  that  it  can  be  hoisted  by  a  derrick- 
hook  when  necessary.  In  most  communities  such  a 
wheeled  apparatus,  which  is  now  widely  used  for  weld- 
ing, can  readily  be  rented  for  a  reasonable  price.  It  is 
shown  on  Plate  No.  33. 


CHAPTER   V 

SPECIFIC    EXAMPLES   OF    UNDERPINNING 

146,  148,  and  150  William  Street 
THESE  buildings  are  of  the  ordinary  five-story 
brick  type  with  isolated  columns,  the  loads  running 
from  20  to  30  tons  each.  The  excavation  line  was  the 
building  line  of  the  building  and  sub-grade  about  16 
feet  below  the  foundations.  This  arrangement  pre- 
cluded the  use  of  a  reenforcing  grillage  because  it  would 
physically  interfere  with  the  future  subway,  so  needling 
was  resorted  to. 

Two  continuous  beds  of  6  x  12  timbers  4  feet  long 
were  placed  on  the  soil,  a  fine-grained  sand,  4  feet  from 
the  front  and  4  feet  from  the  rear  of  each  column,  and 
two  1 8-inch  longitudinal  I-beams  were  placed  on  each 
bed.  Needles  of  1 5-inch  I-beams  on  top  of  the  1 8-inch 
I-beams  were  then  placed  one  by  one  in  niches  carefully 
cut  in  the  brick  columns  to  receive  them.  The  needles 
of  each  column  were  then  lashed  together  to  prevent 
spreading  and  were  wedged  on  the  longitudinal  I-beams 
until  they  relieved  the  footing  stones  of  the  columns 
of  their  loads.  The  lower  parts  of  the  columns  were 
then  cut  away,  and  pits  sunk  on  the  line  of  the  future 
excavation  directly  under  each  column.  This  work 
is  shown  on  Plates  No.  9  and  No.  34. 

58 


SPECIFIC    EXAMPLES    OF    UNDERPINNING 


59 


The  pits  were  sunk  about  18  inches  below  grade; 
a  toe  was  dug  out  18  inches  to  help  prevent  overturn- 
ing and  was  reenforced  with  steel  rods;  then  the  pit 


PLATE  No.  34.     Showing  Exterior  Longitudinal  18"  I-Beams  and    15" 

I-Beam  Needles  with  Lashings  to  Prevent  Spreading 

An  effective  form  of  needling  where  there  is  room  to  place  them  and  where 
the  loads  are  moderate 

concreted.  When  the  concrete  had  set  a  brick  pier 
was  built  up  to  the  original  column,  two  ^-inch  steel 
plates,  or  wedging  stones,  with  wrought-iron  wedges 
between  them,  being  inserted  at  a  convenient  height. 
When  the  mortar  had  set,  the  wedges  were  driven 
until  the  needles  were  relieved  of  their  load.  The 
needles  were  then  removed  and  the  niches  in  the 


60  MODERN    UNDERPINNING 

sides   of    the    columns    bricked    up.       No    settlement 
occurred. 

145-755  William  Street 

This  building  is  a  five-story  brick  structure,  with 
column  loads  of  about  150  tons  each,  and,  with  its 
completed  underpinning,  is  shown  in  Plate  No.  35. 
The  brick  columns,  each  resting  on  a  small  rectangular 
slab  of  concrete,  were  founded  on  sand. 

Ground  water  was  from  one  to  two  feet  below 
the  grade  of  the  subway,  so  that  underpinning  pits 
could  be  sunk  deep  enough  to  render  pile  driving 
unnecessary.  The  design  called  for  concrete  piers 
about  25  feet  deep  and  soil  pressures  of  about  4  tons 
per  square  foot.  The  outside  of  the  subway  was  the 
theoretical  building  line,  which  was  8  inches  inside 
the  face  of  the  brick  columns;  thus  the  underpinning 
piers  would  form  a  masonry  retaining  wall  for  the  sub- 
way excavation,  the  gaps  between  them  being  sheeted 
with  horizontal  sheeting  as  the  excavation  proceeded. 

The  first  step  was  to  place  a  concrete  steel  grillage 
so  as  to  make  the  foundation  of  the  building  con- 
tinuous. This  was  done  by  means  of  1 8-inch  longi- 
tudinal I-beams  placed  close  to  the  columns  and  well 
dowelled  in,  with  cross  I-beams  of  different  convenient 
sizes  placed  in  niches  cut  for  them  in  the  brickwork, 
and  the  whole  concreted,  as  shown  on  Plate  No.  36. 

Pit  sinking  was  then  started,  three  or  four  pits 
being  sunk  at  a  time,  the  ones  under  the  center  of  the 
columns  invariably  being  sunk  last.  The  concrete  in 


PLATE  No.  35.     145-155  William  Street,  Showing  Columns,  Grillage, 

Underpinning  Piers,  and  Toe 

Columns  were  first  connected  by  a  new  grillage  similar  to  that  shown  on 
Plates  Nos.  18,  19,  and  20.  Piers  sunk  beneath  this  grillage  were  wedged 
up  as  per  Plates  Nos.  25  and  37. 


SPECIFIC   EXAMPLES   OF   UNDERPINNING  63 

the  pits  was  left  down  about  2  feet  below  the  grillage, 
and  when  set  was  wedged  up  and  sealed  with  concrete 
and  grout,  pipes  having  been  originally  placed  in  the 
grillage  for  this  purpose,  as  shown  in  Plate  No.  37. 

A  toe,  about  18  inches  wide  and  18  inches  deep, 
reenforced  with  steel  rods,  was  placed  at  the  foot  of 
each  pit  on  the  subway  side,  not  only  to  give  a  larger 
bearing  area,  but  also  to  counteract  the  overturning 
tendency  of  the  high  wall. 

Bank  of  America 

The  Bank  of  America  Building,  on  the  northeast 
corner  of  Wall  and  William  Streets,  shown  on  Plate  38, 
is  a  nine-story  office  building,  of  the  solid  masonry 
construction  that  was  used  thirty  years  ago.  The 
3,000  tons  of  building  on  the  William  Street  side, 
which  had  to  be  underpinned,  were  carried  on  six 
large  brick  columns,  each  with  a  load  of  500  tons. 
The  column  bases,  about  lox  14  feet,  rest  on  a  con- 
tinuous unreenforced  concrete  slab,  about  2^2  feet  thick 
and  12  feet  wide.  The  soil  is  a  very  fine-grained, 
compact  sand  and  clay,  ground  water  is  6  feet  below, 
and  grade  21  feet  below,  the  bottom  of  the  foundation; 
and  the  neat  line  of  the  subway  excavation  was  the 
building  line  of  the  building. 

The  14-inch  steel  concrete  piles,  which  were  jacked 
down  in  the  usual  way,  were  assigned  a  load  of  30  tons 
in  the  design,  and  were  founded  on  a  stratum  of  hard- 
pan  about  29  feet  below  the  foundation.  Every  pile, 


PLATE  No.  38.     Bank  of  America,  Showing  Underpinning 

All  piles  directly  wedged  to  original  foundation  as  per  method  on  Plate  No.  32. 

Concrete  wall  mainly  to  enclose  wedging  securely 


66  MODERN    UNDERPINNING 

after  concreting,  was  tested  to  refusal  with  a  load  of 
80  tons,  and  by  means  of  the  special  pile  cap,  already 
described,  was  wedged  up  to  the  foundations  with 
I-beams  before  the  test  load  was  removed.  In  some  of 
the  pits  five  piles  were  placed — this  was  because  it  was 
thought  some  piles  might  be  buckled  and  lost — however, 
as  this  difficulty  did  not  present  itself  the  number  was 
reduced  to  four,  the  number  required  by  the  design. 

The  first  step  was  to  concrete  in  six  1 5-inch  I-beams, 
about  9  feet  long,  set  X-wise  between  each  pair  of 
columns  in  niches  cut  for  them  in  the  brickwork, 
thus  strengthening  the  foundations  for  the  succeeding 
operations  as  shown  in  Plate  39.  The  4-foot  wide  pits 
were  then  marked  off  and  numbered,  and  pit-sinking 
started.  They  were  sunk  in  sets  of  three  or  four,  well 
distributed  along  the  building,  so  as  to  make  the  settle- 
ment uniform  and  as  small  as  possible,  the  ones  between 
the  columns  being  started  first,  because  there  the  soil 
would  be  under  least  compression.  Each  set  was  com- 
pleted before  the  next  was  started,  and  the  order  of 
sinking  is  given  in  the  accompanying  schedule: 
Set  i  Pit  Nos.  5,  12,  20 
"  2  "  "  8,  16 

"  3    ';    "  4, 13, 21 

"    4      "       "     9,  17,  22 

"    5       "       "     3,  10,  18,  23 
"    6       "       "     2,  6,  n,  19 

11    7      "•       "     i,7,i4 

11    8       "       "     15 


68 


MODERN    UNDERPINNING 


All  pits  were  similar,  so  only  one  will  be  described 
in  detail.  An  approach  pit  down  to  water-level  was 
dug,  the  rear  of  the  pit  being  at  the  building  line,  and  a 


PLATE  No.  40.  Showing  Brick  Columns,  Continuous  Concrete  Base,  V- 
Shaped  Concrete  Enclosing  Crossed  15"  I-Beams,  and  the  Practically 
Completed  Underpinning,  Excavation  for  Subway  Cut  Started 

temporary  pile  was  jacked  down  and  wedged  up,  thus 
replacing  about  40  tons  of  the  bearing  area  lost  in  the 
digging  of  the  pit.  The  original  soil  load  was  about 
3  tons  to  the  square  foot,  about  25  square  feet  of  soil 
was  disturbed,  so  that  probably  75  tons  of  bearing  area 
were  lost,  which  was  compensated  for  by  a  slight 
settlement. 

The   pit  was  then  extended  2  feet  farther,   two  of 


SPECIFIC   EXAMPLES   OF   UNDERPINNING  69 

the  permanent  piles  were  then  driven,  one  of  which 
was  wedged  up  and  the  pit  then  extended  to  its  full 
width,  2^  feet  more.  The  remaining  two  or  three 
piles  were  then  driven,  all  wedged  up  and  the  pit  con- 
creted, holes  being  drilled  through  the  old  foundation 
so  that  the  pit  could  be  grouted  and  a  good  contact 
secured  between  the  pit  concrete  and  the  old  founda- 
tions. Plate  No.  40  shows  a  view  of  the  foundations 
of  this  building  when  the  underpinning  was  practically 
completed  and  the  excavation  of  the  soil  in  front  of  the 
building  started.  Plate  41  is  another  view  showing 
the  temporary  piles  and  the  overhang  of  the  old  foun- 
dations over  the  underpinning. 

When  the  underpinning  was  completed,  the  wedging 
of  the  temporary  piles  was  dismantled  and  the  over- 
hanging part  of  the  old  foundation  was  removed.  The 
occupants  of  the  building  were  hardly  aware  that 
operations  were  going  on,  as  all  the  work  was  done  below 
the  street  and  outside  the  building.  The  settlement  of 
the  building  was  slight  and  very  uniform,  and  there 
was  absolutely  no  damage  to  the  structure. 

National  City  Bank 

The  National  City  Bank  Building  was  formerly 
the  New  York  Custom  House,  but  after  being  taken 
over  by  the  bank  was  remodelled,  the  interior  being 
practically  rebuilt  and  founded  upon  columns  with 
wooden  pile  foundations.  The  exterior  walls  remained 
as  a  sort  of  ornamental  shell,  but  were  run  up  a  few 


SPECIFIC    EXAMPLES    OF    UNDERPINNING  71 

stories  higher.  To  protect  the  exterior  wall  from 
inside  excavations  around  the  inner  perimeter  of  the 
walls  during  the  building  alteration,  a  row  of  heavy 
interlocking  steel  piling  had  been  driven.  The  exterior 
walls  and  their  footings  are  of  granite  resting  upon 
the  sand.  The  footing  is  about  ten  feet  wide  and 
the  load  per  linear  foot  of  wall  about  30  tons. 

The  footings  and  walls  appeared  so  massive  that 
no  attempt  was  made  to  reenforce  them.  A  few  4- 
foot  pits,  spaced  at  wide  intervals  along  the  wall,  were 
started  and  from  them  piles  were  driven  to  hard-pan, 
an  average  distance  of  about  27  feet  and  individually 
wedged  against  the  huge  granite  blocks  of  the  footing. 
The  piles  were  so  spaced  that  the  average  center  line 
would  be  one  foot  from  the  center  of  loading  of  the 
wall.  After  the  first  series  of  pits  were  concreted  and 
sealed,  other  sets  were  started  until  there  was  a  con- 
tinuous 4-foot  wall  of  concrete  under  the  entire  front 
surrounding  181  piles,  about  one  per  running  foot 
of  wall.  Most  of  the  4-foot  pits  were  opened  in  two 
stages  so  as  to  minimize  the  loss  of  bearing  area, 
that  is,  about  two  feet  of  their  width  was  excavated 
and  sheeted,  the  front  row  of  piles  driven,  one  of 
which  was  wedged  up,  and  then  the  pit  enlarged  to 
the  full  width  and  the  rear  row  of  piles  driven. 

Owing  to  the  importance  of  this  building  and  the 
large  interests  involved,  many  tests  were  made  as  to 
the  capacity  of  the  1 4-inch  steel  pile  used.  One  test 
showed  that  the  empty  shell,  only  %4  inches  thick, 


72  MODERN    UNDERPINNING 

held  90  tons  applied  with  a  hydraulic  jack.  Another 
pile,  after  reaching  hard-pan  under  its  first  test  load  of 
90  tons,  settled  only  i  inch  and  held  its  load  absolutely 
without  settlement  for  60  minutes. 

Although  there  was  some  apprehension  with  regard 
to  this  building,  due  to  the  fact  that  it  had  been  ex- 
tensively altered,  and  the  shell-like  nature  of  its 
exterior  wall,  but  little  settlement  and  very  slight 
damage  were  manifest  after  the  underpinning  was 
completed.  The  underpinning  took  four  months.  To 
protect  the  material  between  the  piles  from  flowing 
when  the  subway  excavation  opposite  was  carried  to 
sub-grade,  a  row  of  light  Lackawanna  steel  piling  was 
driven  just  outside  of  subway  structure.  The  Na- 
tional City  Bank  Building  with  its  underpinning  is 
shown  on  Plate  No.  42. 

Lord's  Court  Building 

The  Lord's  Court  Building  is  a  nineteen-story, 
steel-skeleton  structure  at  the  corner  of  William  Street 
and  Exchange  Place.  For  its  foundation  light  spruce 
piles  were  closely  driven  over  the  entire  plot  (pre- 
sumably to  hard-pan),  and  on  them  a  heavy  platform 
of  concrete,  4  feet  6  inches  thick,  was  cast,  the  top 
of  the  piles  being  embedded  in  this  platform  about 
6  inches.  The  piles,  although  in  place  about  25  years, 
were  found  to  be  in  excellent  condition;  the  ground 
water-level  at  the  beginning  of  subway  excavation 
was  near  the  top  of  the  piles. 


PLATE  No.  42.     National   City   Bank  Building,  Showing  Its  Underpinning 

and  the  Subway  Cut 
Piles  extend  to  a  layer  of  hard-pan  10  feet  below  sub-grade 


74  MODERN    UNDERPINNING 

Upon  the  concrete  platform  the  piers  supporting 
the  building  were  founded.  This  platform  with  its 
supporting  piles  encroached  from  one  foot  to  six  feet 
upon  the  future  subway  structure. 

The  underpinning  problem  was  to  find  a  means 
of  substituting  new  piles  for  the  old  ones,  within  the 
limits  of  the  future  subway,  without  endangering  the 
building.  As  sub-grade  was  only  about  8  feet  below 
the  bottom  of  the  concrete  platform,  the  subway  cut 
was  carefully  excavated  by  the  building,  a  protecting 
berm  being  left  adjacent  to  it.  From  this  berm  tem- 
porary concrete-steel  piles,  about  5  feet  on  centers, 
were  driven  underneath  the  edge  of  the  concrete  plat- 
form, and  wedged  up  to  it.  Next,  a  small  strip  of  the 
upper  portion  of  the  berm  was  removed  and  the  mate- 
rial between  the  wooden  piles  carefully  excavated,  so 
that  by  cutting  one  or  two  of  them  a  1 4-inch  steel  pile 
could  be  driven  just  back  of  the  neat  line  of  the 
subway  structure.  A  steel  pile  was  substituted  for 
each  two  wooden  piles  removed.  After. a  strip  about 
15  feet  long  was  so  underpinned,  the  rest  of  the 
berm  was  excavated,  a  form  was  set  up  just  back  of 
the  water-proofing  line  of  the  subway,  and  a  concrete 
face,  about  24  inches  thick,  was  cast  directly  against 
the  bank  and  about  the  steel  and  wooden  piles  exposed. 
It  was  found  that  the  material,  although  previous  to 
draining  a  fine  running  sand,  after  being  drained,  could 
be  cut  down  vertically.  In  this  manner  the  entire 
front  was  passed  safely  without  any  settlement. 


SPECIFIC    EXAMPLES    OF    UNDERPINNING 


75 


The  supporting  value  of  many  of  the  wooden  piles 
was  recovered  for  the  building  by  wedging  between  the 
face  wall,  resting  upon  the  butts  of  the  cut-off  piles 
and  the  concrete  platform  of  the  building. 


PLATE  No.  43.     Showing  Substitution  of  14"  Steel  Concrete  Piles  for  Old 
Wooden  Ones  Which  Had  to  Be  Removed  in  the  Lord's  Court  Building 

Plate  No.  43  shows  the  underpinning  operations. 

The  method  of  replacing  wooden  piles  with  those 
of  concrete  and  steel  is  of  wide  application  to  cases 
where  buildings  are  found  to  be  resting  on  insufficient 
pile  foundations  and  more  especially  where  the  top 
of  the  piles  has  decayed,  due  to  lowering  of  the  ground- 
water  level.  It  would  seem  to  be  practicable  to 


76  MODERN    UNDERPINNING 

replace  the  decaying  wooden  piles  by  permanent  ones 
of  steel  and  concrete.  Each  of  the  new  piles,  if  prop- 
erly tested  and  wedged,  is  easily  as  good  as  three  wooden 
piles.  A  fair  value  of  a  wooden  pile  is  15  tons;  14" 
steel-concrete  pile,  45  tons. 

The  great  advantage  of  the  piles  placed  after  the 
building  is  up  is  that  the  structure  can  be  used  as 
a  reaction  for  driving,  and,  what  is  more  important, 
for  individually  testing  and  loading  the  piles.  Where 
piles  are  driven  in  the  open  there  is  no  good  way  of 
testing  them,  and,  moreover,  those  which  are  not  on  a 
firm  foundation  may  not  work  at  all,  a  few  taking  the 
load,  unless  the  building  settles  sufficiently  to  throw 
the  others  into  bearing  which  might  be  damaging  to 
the  structure.  The  underpinning  of  the  Lord's  Court 
was  looked  forward  to  with  a  great  deal  of  concern 
because  some  of  the  piers  were  cracked  for  nearly 
the  full  height  of  the  building,  due  probably  to  the 
cause  outlined  above.  But  the  underpinning  caused 
no  further  damage  or  settlement. 

135  William  Street 

This  large  seventeen-story  steel  -  skeleton  office 
building,  shown  on  Plate  No.  40  with  its  underpin- 
ning on  the  southwest  corner  of  William  and 
Fulton  Streets,  was  underpinned  entirely  from  out- 
side the  building.  The  six  columns  on  the  William 
Street  front  which  had  to  be  underpinned  were  sup- 
ported by  a  spread  foundation  consisting  of  a  more 


SPECIFIC    EXAMPLES    OF    UNDERPINNING 


77 


*  PLATE  No.  44.     Underpinning    of 
135  William  Street 


or  less  continuous  un- 
reenforced  concrete  mat. 
The  foundation  was  only 
four  feet  above  grade 
and  water  \y2  feet  below 
grade.  The  outside  of 
the  subway  excavation 
was  the  building  line  of 
the  building,  so  that 
about  4^/2  feet  of  the 
old  foundation  that  was 
left  overhanging  the  un- 
derpinning had  to  be 
removed. 

The  first  operation, 
after  stripping  the  foun- 
dations, was  to  reenforce 
the  foundation  by  means 
of  six  X-crossed  1^4 -inch 
reenforcing  rods  con- 
creted in  the  three  gaps 
between  columns.  The 
21  4  x  4-foot  underpin- 
ning pits  were  then  put 
in  in  sets  of  two,  three 

*  Foundations  were  extended 
down  a  few  feet  by  jacking  down 
filled  concrete  piles  into  soft  ground 
beneath  and  wedging  to  original 
foundation.  Projections  of  foun- 
dation to  left  were  later  cut 'off. 


78  MODERN    UNDERPINNING 

and  four  pits  at  a  time,  care  being  taken  to  keep  the  pits 
opened,  at  the  same  time  as  widely  separated  as  pos- 
sible. All  the  pits  were  similar,  so  only  one  will  be 
described. 

Because  of  the  quality  of  the  soil  encountered  at 
water-level,  its  bearing  power  alone  could  not  be  relied 
on,  so  14-inch  steel-concrete  piles  were  used  in  an  un- 
usual way.  A  2-foot  length  was  placed  in  the  pit  and 
concreted.  The  pile  was  then  forced  into  the  ground, 
more  sections  being  added  if  necessary,  until  a  reac- 
tion of  60  tons  was  obtained,  and  the  pile  then  wedged 
up  without  releasing  the  applied  test  load. 

An  approach  pit  was  put  down  so  that  the  rear 
of  the  pit  was  at  the  building  line,  and  usually  a  tem- 
porary pile  was  put  in.  Then  the  pit  was  extended, 
one  pile  driven  and  wedged  up  and  the  pit  again 
extended;  all  piles  driven,  wedged  up,  and  the  pits 
concreted  and  grouted  up.  The  approach  pit  was 
concreted  up  to  sub-grade,  reenforcing  steel  being  first 
placed  so  that  there  was  a  toe  which  gave  a  larger 
bearing  area  and  helped  to  overcome  any  overturning 
moment  that  there  might  be. 

The  Kuhn-Loeb  Building 

The  Kuhn-Loeb  Building  is  a  modern  twenty-one- 
story  building,  constructed  in  1904,  at  Pine  and 
William  Streets,  New  York  City,  and  with  its  under- 
pinning is  shown  on  Plate  45.  Most  of  the  columns 
are  carried  on  I-beam  grillages,  consisting  of  an  upper 


PLATE  No.  45.     Kuhn-Loeb  Building,  Showing  Its  Underpinning 
For  details  see  Plate  No.  42 


80  MODERN   UNDERPINNING 

layer  of  2O-inch  I's,  a  lower  layer  of  1 5-inch  I's  rest- 
ing on  a  3O-inch  bed  of  concrete,  which  in  turn  was 
founded  upon  a  fine  sand  just  above  water-level. 
The  grillages  of  the  exterior  columns  encroached  about 
5  feet  on  the  street.  The  pair  of  columns  adjacent  to 
the  Bank  of  New  York  was  founded  upon  two  large 
5-foot  3-inch  girders,  in  turn  resting  upon  transverse 
I-beams  founded  upon  a  layer  of  concrete. 

To  put  a  subway  through  William  Street  it  was 
necessary  to  cut  off  the  encroaching  foundations,  re- 
move the  vaults  and  boiler  foundations  under  the 
sidewalk;  besides  this,  the  owners  feared  that  to  under- 
pin the  building  it  would  be  necessary  to  occupy  a 
large  part  of  the  interior  of  the  basement,  which  would 
have  seriously  crippled  the  mechanical  plant  of  the 
building.  This  plant,  consisting  of  a  large  hydraulic 
elevator  installation,  boilers,  dynamos,  pumps,  and 
even  a  refrigerating  plant,  was  packed  as  closely  as 
possible  in  the  basement. 

What  further  alarmed  the  owners  wras  that  the 
records  showed,  and  of  this  the  basement  masonry  and 
surrounding  buildings  gave  ample  evidence,  that  from 
the  time  the  foundations  were  laid  to  the  completion 
of  the  building  a  settlement  of  over  two  inches  occurred. 
It  was  feared  that  any  underpinning  would  further 
settle  and  seriously  injure  the  building  and  its  neigh- 
bor, the  Bank  of  New  York. 

The  Kuhn-Loeb  Building  became  the  storm-center 
of  opposition  to  the  William  Street  Subway,  which 


SPECIFIC    EXAMPLES    OF    UNDERPINNING  81 

opposition  defeated  a  projected  subway  through  this 
street  about  ten  years  ago.  However,  the  William 
Street  line  was  an  indispensable  link  in  the  dual-sub- 
way system,  being  the  only  feasible  direct  connection 
to  Brooklyn  for  the  new  tubes  under  the  East  River, 
now  being  built  for  the  Interborough  system. 

The  property-owners  engaged  distinguished  lawyers 
and  engineers  and  most  energetically  opposed  the  City's 
application  to  the  court  to  approve  this  line  after  the 
property-owners  refused  consent.  The  engineers  for 
the  property-owners  built  their  case  mainly  on  the  diffi- 
culties of  the  underpinning  of  the  Kuhn-Loeb  Building, 
and  the  City  retained  experts  to  show  the  practicability 
of  this  underpinning,  and  convinced  the  referees  to 
whom  the  matter  was  referred  as  to  its  feasibility. 

The  experts  for  the  City  submitted  two  methods: 
one  by  compressed  air,  proposed  by  Mr.  F.  L.  Cran- 
ford;  the  other  by  piles,  proposed  by  Messrs.  Breuchard 
and  Goldsborough.  Mr.  Cranford  planned  to  place 
horizontal  air-locks  just  outside  the  foundations  and 
by  their  aid  drive  shafts  through  the  water-bearing 
sand  to  hard-pan  or  rock,  this  shaft  to  be  filled  with 
concrete  and  to  become  supporting  piers  for  the 
building.  This  method  was  expensive,  being  esti- 
mated at  $90,000.  The  other  method  proposed  was  to 
sink  3-foot  cylinders  outside  the  foundations,  these 
cylinders  to  support  longitudinal  girders,  which  in 
turn,  by  means  of  heavy  suspender  rods  attached  to 
flanges  of  the  I-beam  grillages,  were  to  relieve  the 


82  MODERN    UNDERPINNING 

foundations  of  a  portion  of  their  load  so  that  it  would 
be  safe  to  drive  piles  directly  below  them.  This 
method  was  estimated  to  cost  $80,000. 

The  experts  for  the  property-owners  had  difficulty 
in  disputing  either  of  the  two  methods  outlined  by 
the  City's  experts,  and  the  referees  stated  they  had 
confidence  in  the  ability  of  the  engineering  profession 
to  solve  this  problem  when  it  came  to  it,  but  recog- 
nized the  risks  involved  by  requiring  the  City  to 
assume  primary  responsibility  for  damage  done  to 
buildings  by  underpinning  operations  and  the  build- 
ing of  the  William  Street  Subway,  being  the  first  and 
only  time  that  the  City  has  assumed  such  responsibility. 

The  contractor  for  the  William  Street  Subway  bid 
$32,000  for  the  underpinning  of  the  Kuhn-Loeb  Build- 
ing, planning  to  use  a  simpler  method  than  either  of 
the  methods  proposed  by  the  City  before  the  referees. 

Before  starting  operations  the  water-level  was  low- 
ered by  a  sump  and  ditches  sufficiently  to  allow  head- 
room (4  feet)  for  the  driving  of  piles.  Meanwhile, 
the  boilers  were  removed  from  the  vault  under  the 
sidewalk  and  the  foundations  stripped.  No  space 
within  the  building  was  occupied  for  underpinning 
purposes,  the  machinery  inside  being  protected  by  a 
hollow  tile  wall  erected  on  the  building  line. 

It  was  felt  that  by  very  careful  work  it  would  have 
been  entirely  feasible  to  underpin  the  grillages  just 
as  they  stood,  by  gradually  tunneling  below  the  foot- 
ages  and  securely  wedging  piles  to  make  up  for  the 


84  MODERN    UNDERPINNING 

lost  bearing  area.  However,  to  diminish  the  risk  of 
underpinning  and  to  enable  a  large  measure  of  prelim- 
inary support  to  be  obtained  before  actually  going  below 
the  column  footings  a  very  heavy  grillage  was  con- 
structed. This  in  principle  was  merely  the  piecing  out 
the  gaps  between  the  existing  grillages,  as  shown  on 
Plates  Nos.  13,  14,  and  15. 

The  next  step  was  to  open  two  pits  between  the 
old  column  footings  and  to  wedge  two  preliminary 
or  approach  piles  under  the  recently  constructed  gril- 
lage. These  piles  were  loaded  with  about  40  tons 
apiece,  using  pile  cap,  jacks,  and  pair  of  I-beams  de- 
scribed elsewhere.  The  first  pits,  only  large  enough  for 
one  pile  apiece,  were  enlarged  to  provide  for  two  perma- 
nent piles  outside  the  excavation  lines.  One  of  these 
piles  was  wedged  up  and  another  enlargement  pro- 
vided for  the  back  row  of  piles.  After  all  piles  had  been 
wedged  up,  the  pits  were  concreted  in  to  form  part 
of  a  permanent  4  ft.  6  in.  wall  just  back  of  the  building 
line. 

The  piles,  shown  on  Plate  46,  were  driven  so  that 
the  encroaching  portion  of  the  foundations  was  no 
longer  needed  and  could  be  cut  off.  The  whole  con- 
stituted a  system  of  tunneling,  the  footings  being  the 
roof,  the  pile  props  being  good  for  about  90  tons  each. 
It  can  be  readily  seen  that  even  a  twenty-one  story 
building,  with  500  tons'  concentrations,  can  be  readily 
carried  by  piles,  there  being  ample  room  in  any  or- 
dinary case  for  their  driving.  All  the  piles  were  driven 


SPECIFIC    EXAMPLES    OF    UNDERPINNING  85 

to  a  firm  bearing  on  hard-pan  at  an  average  depth  of 
27  feet  below  the  foundations,  and  each  pile  was  very 
carefully  tested  and  wedged  while  loaded,  without 
releasing  its  test  load  of  about  90  tons,  though  only 
assigned  in  the  design  a  load  of  32  tons. 

Some  very  careful  records  made  with  the  Berry 
strain  gauge  showed  that  after  a  pile  was  wedged  a 
portion  of  its  load  was  taken  away  by  the  neighbor- 
ing piles  as  they  were  loaded,  which  would  appear  to 
indicate  a  slight  actual  lifting  of  the  building.  In 
fact,  a  very  careful  level  record  showed  a  very  slight 
settlement  of  the  building  during  the  opening  of  the 
first  pits,  after  which  the  building  was  stationary  and 
even  appeared  to  rise  very  slightly  during  underpin- 
ning operations.  A  piano-wire  plumb  line,  14  stories 
high,  suspended  to  the  side  of  the  building  and  kept 
under  observation  during  the  underpinning  operations, 
showed  no  movement  whatever  relative  to  the  build- 
ing. The  building  was  absolutely  undamaged.  When 
we  remember  that  this  was  the  tallest  building  ever 
underpinned  and  the  doleful  predictions  made,  we  may 
say  that  great  progress  in  this  class  of  work  was 
demonstrated. 

Underpinning  Elevated  Railroad  Columns 

Many  elevated  railroad  columns  have  been  under- 
pinned in  New  York  with  no  serious  accidents  and 
without  inconvenience  to  traffic.  Very  many  different 
methods  have  been  used  for  temporarily  carrying  the 


86 


MODERN    UNDERPINNING 


columns,  with  their  ten-train  loads,  while  the  new 
foundations  were  being  built,  and  the  following  one 
is  the  result  of  many  trials  and  has  been  widely  used 
by  contractors. 

A  typical  problem   was   to   support   two  elevated 


PLATE  No.  47.     Showing  Method  of  Temporarily  Carrying  Elevated  Railroad 

Columns 

Tower  shown  is  carried  by  concrete  steel  piles  extending  below  sub-grade, 
as  per  Plate  No.  48 

columns,  having  loads  of  approximately  80  tons  each, 
while  the  subway  trench  was  dug  to  about  30  feet  below 
curb,  and  the  subway  structure  itself  built,  when  the 
column  could  be  placed  on  the  subway  roof  which 
was  designed  for  that  purpose. 


88  MODERN    UNDERPINNING 

The  method  used  was  to  drive  two  groups  of 
four  14-inch  steel  concrete  piles  for  each  column. 
This  was  necessary  because  water-level  was  about  10 
feet  below  curb  and  it  was  impracticable  to  get  pits 
down.  These  piles  were  driven  about  5  feet  below 
the  sub-grade  of  the  future  excavation  from  the  street 
surface  in  shallow  pits,  and  were  in  such  a  position 
as  not  to  touch  the  steel  of  the  subway  structure. 
When  concreted,  each  group  was  capped  with  a  small 
concrete  cap,  reenforced  with  ^-inch  reenforcing  rods 
to  tie  the  piles  together.  The  piles  which  were  loaded 
to  about  10  tons  each  of  live  and  dead  loads  carried 
the  "A"  frame  which  supported  the  column  and  ele- 
vated structure,  the  details  of  which  are  shown  on  the 
accompanying  Plates  Nos.  47  and  48. 

One  of  the  features  of  this  frame  is  that  the  legs 
of  the  "A'*  are  free  to  slide  on  the  I2xi2-inch  sill,  but 
are  prevented  from  moving  apart  by  the  four  2^x3- 
inch  iron  straps  which  react  through  the  4-inch  steel 
pin,  which  in  turn  is  held  in  position  by  an  iron  block 
firmly  bolted  to  the  legs  of  the  "A."  When  settle- 
ment occurs  from  time  to  time  from  any  reason,  the 
pins  can  be  jacked  down,  and,  by  bringing  the  legs 
closer  together,  take  up  such  settlement. 


APPENDIX 

UNDERPINNING   IN    ROCK 

ROCK  excavation  gives  rise  to  underpinning  prob- 
lems differing  somewhat  from  those  described  in 
previous  chapters,  but  the  differences  are  not  quite 
enough  to  require  extensive  treatment.  Buildings 
alongside  of  an  excavation  may  be  either  on  a  cover  of 
earth  above  the  rock  or  wholly  or  partly  on  the  ledge. 
The  worst  conditions  exist  where  the  building  is 
founded  on  rock  tending  to  slide  into  the  excavation. 

If  a  building  is  founded  on  rock  and  it  is  felt  that 
this  rock  is  insecure,  then  new  piers  have  to  be  carried 
down  to  sub-grade  or  until  a  secure  rock  stratum  is 
reached.  The  process  is  simple,  although  tedious,  and 
in  some  cases  costly.  Small  shafts  are  sunk  directly 
below  the  building  to  a  proper  depth  in  the  rock  and 
filled  with  concrete  upon  which  the  building  is  wedged. 
The  great  advantages  of  underpinning  a  building  to 
rock  is  that  no  pier  will  suffer  any  settlement  and  can 
carry  a  very  heavy  load,  a  4  x  4-foot  pier  being  good 
for  at  least  400  tons,  while  on  ordinary  earth  it  would 
be  good  for  only  80  tons.  It  is,  therefore,  advantageous 
in  rock  to  strengthen  the  foundation  with  a  heavy 
grillage  so  as  to  take  advantage  of  the  great  bearing 
value  of  rock  and  to  save  expense  and  time  by  sinking 

only  a  few  shafts. 

89 


90  APPENDIX 

The  largest  building  known  to  the  authors  founded 
upon  rock  and  requiring  underpinning  is  the  Metro- 
politan Opera  House,  a  subway  passing  close  to  both 
the  Broadway  and  Seventh  Avenue  fronts.  On  the 
Seventh  Avenue  side  the  rock  was  of  a  treacherous 
character.  The  main  cut  was  driven  by  the  adjacent 
wall  of  brick,  leaving  several  feet  of  rock  berm  adjacent 
to  the  building.  Then  narrow  shafts  were  sunk  under- 
neath this  wall,  which  readily  bridged  over  small 
openings.  Each  shaft  was  filled  with  concrete  and 
wedged  to  the  brick  wall  till  a  new  continuous  wall 
approximately  to  sub-grade  was  formed,  after  which 
it  was  safe  to  complete  the  excavation.  The 
Broadway  side  of  the  building  was  founded  upon 
huge  isolated  brick  piers.  At  the  side  of  each  pier 
and  a  few  feet  below,  the  rock  was  excavated  in  shallow 
shafts  and  concrete  placed  so  as  to  form  an  arch 
spanning  a  shaft  sunk  directly  below  the  center  of  each 
pier  to  subgrade.  Later  the  shaft  was  filled  with  con- 
crete, forming  a  pier  to  which  the  footing  was  wedged. 

Where  the  side  of  a  rock  cut  is  ragged  and  subject 
to  disintegration  or  slides  so  as  to  endanger  buildings 
alongside,  a  concrete  wall  cast  directly  against  the  face 
of  the  rock  is  often  very  effective  and  economical.  Such 
walls  are  much  more  readily  braced  than  the  usual 
rock  face  and  often  give  warning  of  an  imminent  slide 
by  the  cracks  which  would  form  and  which  would  be 
readily  discernible. 


APPENDIX  91 

SPECIAL   ARRANGEMENT   OF   PIT   BOARDS 

In  some  instances,  where  mealy  running  sand  or 
where  there  is  a  small  amount  of  water  encountered, 
openings  may  be  left  between  successive  pit  boards 
when  horizontal  sheeting  is  used.  These  openings 
may  be  formed  in  several  different  ways,  such  as  boring 
holes,  chopping  slots  in  the  boards,  separating  boards 
by  small  wooden  spacers  nailed  on  the  tops  or  sides 
of  the  horizontal  boards.  This  permits  the  packing  of 
sand,  hay,  straw,  mortar,  moss,  or  other  material  to 
prevent  the  loss  of  ground. 


INDEX 

Amount  of  underpinning  done  on  new  subway  system,  3 
"A"  frame  for  elevated-railroad  columns,  86,  87,  88 
Appendix,  89 

Burning  apparatus,  34,  57 

Bank  of  New  York,  37,  38 

Bulk  of  pressure,  55 

Bank  of  America,  63,  65,  66,  67,  68,  70 

Compressed-air  caissons  for  underpinning,  9,  81 
Composite  needle-beam,  26,  27,  28 

Dowels,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,  41,  42 

Examination  of  buildings  to  be  underpinned,  13 

Earth  augers,  51 

Elevated-railroad  columns,  underpinning  of,  85,  86,  87,  88 

Foundations,  29,  30,  33,  37,  60,  63 

Grillages,  29,  31,  32,  33,  34,  35,  36,  37,  38,  39,  4<>,  41,  60,  61,  62,  63,  64,  80,  84 

Hammering  rig,  50 

Jacking  piles,  50,  51,  52,  53,  54,  55,  56 

Kuhn-Loeb  Building,  33,  34,  35,  36,  42,  7»,  79,  80,  81,  82,  83,  84,  85 

Lattice  girders,  40,  41 
Loads  on  piles,  84,  85 
Lord's  Court  Building,  72,  74,  75,  76 

Mucking  piles,  51,  52,  53 

National  City  Bank,  69,  71,  72,  73 

Needles  and  needling,  7,  19,  21,  22,  23,  25,  26,  27,  28,  58,  59 

One  hundred  and  thirty-five  William  Street,  76 
One  hundred  and  forty-six  to  fifty  William  Street,  58 
One  hundred  and  fifty-five  William  Street,  60 
Orange-peel  buckets,  10,  51,  53 


,?4-  INDEX 

Payment  for  underpinning,  3-5 

Piers,  47 

Piles  (steel  concrete),  43,  48,  49,  50,  51,  52,  53,  54,  55,  63,  67,  71,  74,  76,  82, 

84,  87,  88 

Pile  driving,  48,  50,  51,  52,  53,  54 
Pile-settlement  curve,  55 

Pits,  43,  44,  45,  59,  60,  61,  62,  66,  71,  77,  82,  83 
Plumb  bob,  85 
Protection,  10 
Prices  for  underpinning,  3,  4,  81,  82 

Reenforcing  rods,  31,  32,  33,  34,  35,  36,  37,  42,  77 
Replacing  wooden  piles  with  steel  concrete  piles,  75 
Rock  underpinning,  89 

Sheeting  pits,  43,  44,  45,  91 
Shores,. 7,  8,  19,  20,  21,  22 
Strength  of  pile  pipe,  71,  72 

Testing  piles,  54,  55,  56 

Underpinning  defined,  4 
Underpinning  below  water-level,  14 
Underpinning  and  protection  combined,  ii 
Underpinning  plans,  62,  67,  83,  87 

Walls,  reenforcement  of,  37 

Water  jetting,  53 

Wedging,  45,  46,  47,  54,  55,  56,  59,  64,  68,  69,  70,  71,  75,  78,  85 

Woodbridge  Building,  31,  32 

Wood  piles,  72,  74,  75,  76 


SIMMONS' 

Sectional  Concrete  Piles 

Are  Supporting  New  York  Skyscrapers 


Tapered  Ringed 
Sleeve 


For  underpinning, 
and  where  headroom 
is  limited,  piles  of  any 
ultimate  length  can 
be  built  up.  They  can 
be  hammered,  jacked, 
or  jetted  in  place. 

The  sections  can  be 
made  from  about  4  to 
20  feet  long,  to  suit 
the  conditions. 

We  carry  in  stock  a 
complete  assortment 
of  these  sections,  to- 
gether with  our  pat- 
ented sleeves  and 
driving  points. 

Write  for  Booklet 

Pipes,  Fittings,  Valves,  Tools, 
and  Specialties  for  Contractors, 
Engineers,  Waterworks  and  In- 
dustrial Plants 


JOHN  SIMMONS  CO. 

110  Centre  Street  NEW  YORK 


Pat.  Nov.  30, 1915 


Scalloped  Ringed 
Sleeve 


Pat.  Nov.  30,  1915 


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